Patent Publication Number: US-2023147887-A1

Title: Fabrication of thin-film encapsulation layer for light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Pat. Application Serial No. 17/305,963, filed Jul. 19, 2021, which is a continuation of U.S. Pat. Application Serial No. 16/546,006, filed Aug. 20, 2019, now U.S. Pat. No. 11,088,035, issued on Aug. 10, 2021, which is a divisional of U.S. Pat. Application Serial No. 15/802,325, filed Nov. 2, 2017, now U.S. Pat. No. 10,811,324, issued on Oct. 20, 2020, which is a continuation of U.S. Pat. Application Serial No. 15/416,931, filed Jan. 26, 2017, now U.S. Pat. No. 10,586,742, issued on Mar. 10, 2020, which is a continuation of U.S. Pat. Application Serial No. 15/279,261, filed Sep. 28, 2016, now U.S. Pat. No. 9,806,298, issued on Oct. 31, 2017, which is a continuation of U.S. Pat. Application Serial No. 14/627,186, filed Feb. 20, 2015, now U.S. Pat. No. 9,496,519, issued on Nov. 15, 2016, which is a continuation of U.S. Pat. Application Serial No. 14/458,005, filed Aug. 12, 2014, now U.S. Pat. No. 8,995,022, issued on Mar. 31, 2015, which claims benefit from U.S. Provisional Pat. Application Serial Nos. 62/019,076, filed Jun. 30, 2014; 62/005,044, filed May 30, 2014; 61/977,939, filed Apr. 10, 2014; and 61/915,419, filed Dec. 12, 2013, all of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Various chemical and physical deposition processes can be used to deposit materials over a substrate. Some deposition processes rely on patterned deposition, where a mask or other mechanism is used to create nanoscale features within precise tolerances, for example, matching dimensions of electronic nanoscale structures such as transistor path widths, while other deposition processes provide relatively featureless, large scale deposition, such as blanket based coatings or depositions that span tens of microns of distance or more. 
     There exists a class of fabrication applications for which existing processes are suboptimal. More specifically, for applications where one desires to form a layer over a large region of the substrate relative to nanoscale features, particularly for organic materials deposition, it can be difficult to control uniformity of the deposited layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a diagram showing an embodiment of disclosed techniques, in which thickness data for a desired layer is converted to a halftone pattern useful for fabricating the desired layer. 
         FIG.  1 B  is an illustrative diagram of a process in which layout data describing a desired layer is generated or received, converted into a halftone pattern, and used to deposit ink that will become a desired layer. 
         FIG.  1 C  is a block diagram of a detailed embodiment, where thickness data is used to obtain grayscale values for respective “print cells,” and where the grayscale values are then used to generate a halftone pattern. 
         FIG.  2 A  provides an illustrative view showing a series of optional tiers, products or services that can each independently embody techniques introduced herein. 
         FIG.  2 B  provides a plan view of a fabrication mechanism that can be used to fabricate a component, for example, a flat panel device in presence of a controlled atmospheric environment. 
         FIG.  2 C  is a plan view showing layout of a printer within the fabrication mechanism of  FIG.  2 B ; more specifically,  FIG.  2 C  shows how a print head  259  is moved relative to a substrate  253 . 
         FIG.  2 D  is a block diagram of various subsystems associated within a printing module of  FIG.  2 A . 
         FIG.  3 A  shows a way of defining a waveform used to create an individual ink droplet according to discrete waveform segments. 
         FIG.  3 B  shows an embodiment where droplets having different parameters can be created based on different nozzle firing waveforms. 
         FIG.  3 C  shows circuitry associated with generating and applying a desired waveform at a programmed time (or position) to a nozzle of a print head; this circuitry provides one possible implementation of each of circuits  343 / 351 ,  344 / 352  and  345 / 353  from  FIG.  3 B , for example. 
         FIG.  4 A  provides a flow chart used to describe conversion of data representing thickness of a desired layer to a halftone image. 
         FIG.  4 B  provides another flow chart used to describe conversion of data representing thickness of a desired layer to a halftone image. 
         FIG.  4 C  is a flow diagram associated with halftoning calibration. 
         FIG.  4 D  is a flow diagram associated with droplet measurement and qualification. 
         FIG.  5 A  shows one halftone pattern representing a specific ink volume for a print cell. 
         FIG.  5 B  shows another halftone pattern representing a specific ink volume; more particularly,  FIG.  5 B  is used, relative to the halftone pattern of  FIG.  5 A , to discuss frequency modulated (“FM”) halftoning. 
         FIG.  5 C  shows another halftone pattern representing a specific ink volume; more particularly,  FIG.  5 C  is used, relative to the halftone pattern of  FIG.  5 A , to discuss amplitude modulated (“AM”) halftoning. 
         FIG.  5 D  shows the optional use of complementary (or “stitched”) halftone patterns for adjacent tiles. 
         FIG.  5 E  shows a halftone pattern where droplet size (or shape) has been varied to compensate for a misfiring adjacent nozzle. 
         FIG.  5 F  shows a halftone pattern where droplets have been “borrowed” by one nozzle to compensate for a misfiring adjacent nozzle. 
         FIG.  6 A  is a chart showing grayscale values assigned to different print cells in dependence on thickness data. 
         FIG.  6 B  is another chart showing grayscale values assigned to different print cells in dependent on thickness data, but with grayscale corrections added in to smooth or correct error in resultant film thickness. 
         FIG.  7 A  provides a graph used to explain how different halftone droplet densities are associated with different grayscale values to produce desired layer thicknesses. 
         FIG.  7 B  schematically depicts one or more border regions of a substrate, and how halftoning and/or grayscale selection can be varied in the border regions to mitigate edge build-up. 
         FIG.  7 C  shows one possible scheme for halftoning near a border region, more particularly, for use at a corner of a deposited layer. 
         FIG.  7 D  shows edge enhancement of a print cell to provide a consistent layer edge. 
         FIG.  7 E  shows the use of both border adjacent halftone variation, to avoid edge buildup, and “fencing” to improve edge linearity. 
         FIG.  8 A  shows a substrate  801  that will be arrayed into multiple flat panels, for example, multiple organic light emitting diode (“OLED”) display panels, solar panels, or other types of panels. 
         FIG.  8 B  shows the substrate of  FIG.  8 A  after active elements and electrodes have been added to the substrate of  FIG.  8 A . 
         FIG.  8 C  provides a cross-sectional view of the substrate of  FIG.  8 B , taken along lines C-C from  FIG.  8 B . 
         FIG.  8 D  shows the substrate of  FIG.  8 C  after encapsulation ( 840 ) has been added;  FIG.  8 D  also provides a close up showing that the encapsulation ( 840 ) can be formed of many individual layers, such as alternating organic and inorganic layers. 
         FIG.  8 E  shows the substrate of  FIG.  8 D  in a plan view (i.e., from the same perspective as  FIG.  8 B ). 
         FIG.  9    is a block diagram of one process for depositing an organic encapsulation layer. 
     
    
    
     The subject matter defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read in conjunction with the accompanying drawings. This description of one or more particular embodiments, set out below to enable one to build and use various implementations of the technology set forth by the claims, is not intended to limit the enumerated claims, but to exemplify their application. Without limiting the foregoing, this disclosure provides several different examples of techniques for fabricating a materials layer using halftoning to control ink droplet density in a manner that will produce a desired thickness of the deposited layer. These techniques can be embodied as software for performing these techniques, in the form of a computer, printer or other device running such software, in the form of control data (e.g., a print image) for forming the materials layer, as a deposition mechanism, or in the form of an electronic or other device (e.g., a flat panel device or other consumer end product) fabricated using these techniques. While specific examples are presented, the principles described herein may also be applied to other methods, devices and systems as well. 
     DETAILED DESCRIPTION 
     This disclosure provides techniques for fabricating a layer on a substrate using a printing process. More specifically, data representing layer thickness is received and translated using halftoning to produce an ink jet droplet pattern. The ink is a viscous material such that droplets spread to a limited extent and, thus, the more droplets deposited per unit area (i.e., per cell location) the greater the thickness of the resultant layer. 
     In some embodiments, layer thickness is first converted to a grayscale value for each of a number of “print cells,” with each print cell representing a unit area of substrate that has a common thickness value. For example, each print cell can be the smallest unit area representable by a dedicated thickness value. The gray scale values are then used to generate halftoning in a manner that will result in ink droplet density which produces the desired thickness. Note that this intermediate step of using print cells to locally represent thickness is optional. 
     In other embodiments, these processes are used to produce an encapsulation layer that will provide a barrier to prevent exposure of a substrate to materials such as oxygen and water. Halftoning can be selected to yield a continuous layer (i.e., after drop spreading, the deposition area in question is completely covered with ink, with no holes or voids) but with a variable ink volume (and associated, resultant variable thickness). Note that the halftoning can be expressed or applied in a number of manners, using single print head passes, multiple print head passes, and/or any other techniques that use multiple droplets at respective droplet locations to control the aggregate volume of a deposited ink. 
     A number of further, optional implementation variations can be applied to the techniques introduced above. First, calibration processes can be used (given variation in ink viscosity or other factors for example) to map different layer thicknesses to different grayscale values. To provide an introductory example, if it is desired to deposit a layer of 5.0 microns uniform thickness, this thickness data can first be converted to a grayscale value (e.g., a number within the range of 0-255 such as the number “103”) with the number “103” being pre-associated with a given halftone droplet density that, given the ink in question and other process particulars, will produce a 5.0 micron-thick layer following printing and any associated cure process). Generally speaking, halftoning is performed as a single operation for an entire substrate area in question, but this process can also optionally be separately performed for respective “tiles” of a deposited layer, with halftone selection performed for each tile in a manner such that tiles have complementary droplet patterns so as to permit “seamless” stitching together of adjacent droplet patterns (i.e., to avoid Mura effect). Second, any one of a number of error correction processes can be applied to help ensure uniformity of a deposited layer. These variations will be further discussed below. 
     Thus, in one embodiment, desired layer thickness is first specified as an input. This thickness can optionally be first converted to a grayscale value, e.g., a value such as a percentage, e.g., “50%” or another relative ink volume measure. For example, in one contemplated implementation, a correlation between volume of applied ink and desired thickness will have been empirically determined in advance, and so, selecting such a value results in effective selection of a volume of ink that will build the desired thickness; it is also possible to use periodic calibration or dynamic measurement with feedback to arrive at a linkage between any desired thickness and the volume of ink that will ultimately produce the desired thickness. The conversion step can be performed for each of multiple print cell locations that will form part of the deposition area, optionally to develop a grayscale image representing an aggregation of the grayscale values of the respective print cells (see e.g., the discussion of  FIGS.  6 A and  6 B , below). Based on these values, a halftone pattern is then selected or generated where the halftone pattern will result in the desired layer thickness resulting after any cure process for the deposited material. Note that the print cells can have any size relative to a halftone grid that is pertinent to the particular implementation. For example, in one embodiment, the print cells are small, having one or more print cells per halftone grid point (i.e., per possible halftone droplet). In another embodiment, print cells are relatively large, i.e., with many halftone grid points per print cell. A halftoning algorithm can be invoked to generate a droplet pattern that will produce the desired thickness, e.g., with droplets having relatively large dot gain, but with relatively sparse droplet ejections across halftone grid points; thus, even though every print cell might have a grayscale value of “103” (e.g., corresponding to a hypothetical desired layer thickness of 5.0 microns), not every associated halftone grid point will necessarily feature a droplet ejection. 
     Two specific non-limiting applications discussed below respectively use these techniques to regulate thickness of an encapsulation layer for organic light emitting diode devices (“OLEDs”) and solar panels. In these applications, it is typically desired that an encapsulation layer should be impermeable to oxygen and water. Thus, the techniques just discussed can optionally be used to fabricate the encapsulation layer so as to provide that impermeability. Note that the general techniques can also be applied to deposition of other types of materials, organic and inorganic, and to the fabrication of other types of layers (e.g., other than encapsulation layers) and other types of devices. The disclosed techniques are especially useful for the deposition of materials which are to be deposited by liquid or other fluidic deposition processes (e.g., in the form of fluidic ink, whether liquid or vapor); for example, these techniques may readily be applied to depositions of organic materials suspended in a liquid medium. Note also that a typical deposition process deposits only one ink to build each layer (e.g., the layer is effectively monochromatic); this however is not required for all embodiments, and it is also possible to use multiple inks (for example, the mentioned processes can be used to deposit different light generating materials in three respective, fluidically isolated “pixel wells” associated with generation of red, green and blue component light for each image pixel of an OLED display panel, such as used in some televisions). Also note that the term “layer” is used in multiple senses, e.g., an encapsulation layer typically includes one or more constituent film layers, with the individual film layers as well as the aggregate each being an encapsulation “layer.” 
     As used herein, the term “halftoning” refers to the process of generating or selecting a pattern of multiple droplets to apply a variable amount of ink responsive to desired layer thickness for a unit area (e.g., per print cell, per substrate or per unit of substrate area), with a “halftone pattern” being the pattern created by that process. In a typical embodiment discussed herein, halftoning is performed based on one or more grayscale values to produce a halftone pattern that locally represents layer thickness using a droplet pattern of variable droplet density (i.e., dependent on local grayscale value or a locally-weighted function of grayscale values), with each droplet position in a halftone grid being expressed as a Boolean value (i.e., 1 bit); each Boolean value (bit) denotes whether or not a nozzle is to eject a droplet at that position. A “halftone print image” represents a halftone pattern representing the entire print area. A “grayscale value” refers not to color (e.g., white versus gray versus black), but to a value that represents a variable layer thickness measure for a unit area of substrate that is to receive printing; for example, in one embodiment, a “small” grayscale value implies that a given print cell will receive a relatively small volume of ink (e.g., low density of droplets), corresponding to a relatively thin layer thickness for an area represented by the given print cell, while a “large” grayscale value implies that a given print cell will receive a larger volume of ink (relatively high density of droplets) corresponding to a thicker layer. Because layer thickness equals ink volume per unit area, grayscale value is used in many embodiments herein to specify layer thickness for a given unit area. Each grayscale value is typically a multi-bit value, e.g. 8 or 16 bits, but his need not be the case for all embodiments. A “grayscale pattern” is a pattern of any one or more grayscale values, whereas a “grayscale print image” or “grayscale image” is a grayscale pattern representing the print area, e.g., the substrate. A grayscale print image typically features an array of values that are each multi-bit (i.e., grayscale values) where each value represents layer thickness per a corresponding unit area; by contrast, a halftone print image typically features an array of single bit values that each represent whether or not an individual droplet will be ejected at a specific position. For many embodiments discussed below, particularly those geared to producing impermeable layers or layers with uniform thickness, halftone patterns used for printing are typically chosen (given dot gain/ink spreading) to produce a continuous layer, without holes or voids, though with different ink volumes. Note that in such applications, the inks in question typically comprise a monomer, a polymer, or a solvent that suspends a material, with the ink being dried, cured or otherwise processed after deposition so as to form the desired layer thickness as a permanent layer. 
       FIGS.  1 A- 1 C  are used to introduce several embodiments of the techniques introduced above. 
       FIG.  1 A  illustrates a first embodiment  101 . Data is received representing a layer that is to be deposited over a substrate, as indicated by numeral  103 . The substrate can be any underlying material or support surface, for example, glass or another surface, with or without previously deposited structures (e.g., such as electrodes, pathways or other layers or elements); it is not required that the underlying substrate be flat. Note that the received data will typically be presented as part of an electronic file representing a circuit or structure to be fabricated and, for the layer to be deposited, typically includes data defining x-y plane boundaries of the layer and data representing thickness at various points across the desired layer or within a structure of such a layer, for example, in a pixel well. To provide a non-limiting example, the underlying substrate could be an organic device such as an organic light emitting device or organic light emitting diode (“OLED”) display panel in an intermediate state of fabrication, and the received data could indicate that the layer is to be part of an encapsulation of an active region of the OLED display that will seal that region against oxygen and water. The received data in such an encapsulation example would typically indicate where the particular encapsulation layer starts and stops (e.g., x and y edge coordinates) and its thickness as a height (e.g., a z-axis thickness of “5.0 microns”), with the height expressed as thicknesses for one or more various points. In one example, this layer data includes a thickness value for each point on an x-y grid system, though this is not required for all implementations (e.g., other coordinate systems could be used, and thickness for example could be expressed as a single uniform value, as a gradient, or using other means). As indicated by numeral  105 , the received data is, using processes described herein, converted to a halftone pattern that will be used to influence deposition of layer material using a printing process, e.g., an ink jet printing process, to produce the desired layer thickness. Whether or not desired layer thickness is provided on a point-by-point basis, the thickness data is derived for each print cell that will be addressed by the printing process, and is then used to select a specific halftone pattern whose resultant droplets “build” the layer in question. Note that the relationship between print cell and halftone grid (i.e., droplet density) is arbitrary. In one embodiment, each print cell equates to a specific grid point, i.e., there is a one-to-one relationship. In a second embodiment, each print cell corresponds to more than one grid point (i.e., an integer or non-integer number of grid points). In yet a third embodiment, each grid point corresponds to a more than one print cell (i.e., an integer or non-integer number of print cells). Per dashed-line box  106  and as mentioned already, in one embodiment, the halftone pattern is optionally constrained to always produce a locally continuous film, though with variable ink volume dependent on desired layer thickness. The halftone patterns can be optionally determined in advance (e.g., with one to many halftone patterns that could be used per grayscale value or average of grayscale values), for example, so as to provide a capability to vary pattern selection; in another embodiment, droplet density is calibrated as a function of average grayscale value and is used “on the fly” to determine halftone patterning representing a set of grayscale values. In one embodiment, a set of grayscale values, each multi-bit, provides an input to halftone selection software, which then returns an output halftone pattern (e.g., with droplets positioned relative to a halftone grid, and with the decision to fire or not fire a droplet at a given grid point expressed as a single bit). The halftone pattern can be expressed as printer instructions (e.g., a print image to control a printer to print droplets at specific locations). These instructions contain information that will responsively cause the ink jet printing process to deposit ink at volume per unit area that is locally varied according to the information represented by the halftone pattern, with a greater aggregate print cell ink volume for thicker layers, and a lesser aggregate print cell ink volume for thinner layers. 
     Box  110 , and media graphic  111 , represent that, in one embodiment, the steps just introduced can be embodied as instructions stored on non-transitory machine-readable media, e.g., as software. “Non-transitory machine-readable media” means any tangible (i.e., physical) storage medium, irrespective of how data on that medium is stored, including without limitation, random access memory, hard disk memory, optical memory, a floppy disk or CD, server storage, volatile memory and other tangible mechanisms where instructions may subsequently be retrieved by a machine. The machine-readable media can be in standalone form (e.g., a program disk) or embodied as part of a larger mechanism, for example, a laptop computer, portable device, server, network, printer, or other set of one or more devices. The instructions can be implemented in different formats, for example, as metadata that when called is effective to invoke a certain action, Java code or scripting, code written in a specific programming language (e.g., as C++ code) or a processor-specific instruction set, or in some other form; the instructions can also be executed by the same processor or different processors, depending on embodiment. For example, in one implementation, instructions on non-transitory machine-readable media can be executed by a single computer and, in other cases as noted, can be stored and/or executed on a distributed basis, e.g., using one or more servers, web clients, or application-specific devices. 
     The halftoning produced by the process of box  110  can be employed immediately and/or stored for later use. To this effect,  FIG.  1 A  shows that halftoning can be stored as a printer control file  107  (e.g., printer control instructions), for example, also on non-transitory machine-readable media  113 . This media can be the same media as represented by media graphic  111 , or different media, e.g., the RAM or hard disk of a desktop computer or printer, a disk, or a flash card. As a non-limiting example, such printer control instructions could be made available as a network-stored reference design which is adapted for download or transmission to an electronic destination. For most applications, as indicated by optional process block  109 , the applied halftoning will ultimately be used to deposit a layer using the mentioned ink jet printing process. Once the layer deposition steps (and any post-deposition curing or other finishing steps) are complete, the deposited layer in the region of deposition will have a thickness that corresponds to the intended layer thickness, as a function of the halftoning. 
       FIG.  1 B  is an illustrative diagram showing a process and hardware for fabricating a layer, such as the layer just discussed with reference to  FIG.  1 A . The process and hardware are generally represented by numeral  151  and are seen to include one or more computers  153  that are able to receive layout data for one or more layers of material (e.g., as part of a design file). This layout data and any associated design file are generated by and received from a computer  155 , for example a computer used for computer-assisted design (“CAD”). The received layout data (including any design file) can be part of instructions or data stored on machine-readable media where the data or instructions can be used to fabricate the desired component, for example, a consumer electronic product or another product. The layout data is optionally received over a network  157 , for example a local area network (“LAN”) or wide area network (“WAN,” such as the Internet or a private network of a company). In some embodiments, the computer  155  is optionally itself one of the one or more computers  153 , i.e., design of the layer and generation of printer control instructions can optionally be performed on one computer or within a single local network. The one or more computers  153  apply processing as introduced above, that is, to convert thickness data for a layer to at least one halftone pattern. The results of halftoning are stored in local memory  159  and are optionally transmitted to an ink jet printing mechanism  161  via network  163 . Note that the one or more computers  153  can also be combined with the inkjet printing mechanism, e.g., these elements can be embodied as a control terminal for a fabrication mechanism that includes an ink jet printer that will form the desired layer, e.g., as one or more scans that print the layer, each scan as a single pass over an area of substrate, to deposit the desired layer thickness, e.g., following any cure or finishing procedure. The ink jetted by the ink jet printing mechanism typically includes a material (e.g., an organic material) jetted as a fluid, as mentioned. As introduced above and as further described below, in some embodiments, each print cell corresponding to the unit printable area of the substrate is assigned a discrete ink volume (e.g., in the form of a grayscale value). The size of a print cell is arbitrary and typically represents the minimum unit of substrate area that can or will be assigned a discrete thickness (i.e., grayscale value). Each print cell in turn is typically associated with one or more points on a grid where the points of the grid each represent possible, respective ink droplet positions. The firing of each possible droplet is controlled responsive to applied halftoning. In one embodiment, “frequency modulated” halftoning is used, meaning that the firing of droplets from respective print head nozzles (or positions) is performed at a specific spatial frequency, varied according to the desired layer thickness (e.g., see  FIG.  5 A ). In another embodiment, “amplitude modulated” halftoning is used, that is, where droplet firings are in spatially-separated clusters, with the number of droplets per cluster varied according to desired thickness; thus a darker image (i.e., thicker layer) is represented by bigger apparent drops than a thinner layer, again in this embodiment, with dot gain sufficient to achieve a locally continuous film notwithstanding grid points where droplets are not fired (e.g., see  FIG.  5 C ). In still other embodiments, droplet size and/or shape can be varied (e.g., from circular or elliptical or some other shape) by changing the electrical pattern used to fire one or more ink jet nozzles; alternatively or in addition, the halftone pattern and/or printer instructions can instruct multiple passes of a specific scan position by an ink jet print head. Finally, other techniques can also be used, alone or in combination with the techniques mentioned above. These optional features are represented by optional process block  165 . 
     The processing of inputted layout data results in layer thickness data being identified for each print cell and, then, being converted to a grayscale value representing the particular print cell. For example, in one embodiment, the grayscale value is an eight-bit field having 256 possible values; if layer thickness were to range between one micron and eleven microns, then a thickness measure representing six microns (i.e., exactly intermediate thickness in the range) might be converted to the grayscale value “128.” A halftone pattern (e.g., representing a locally continuous film) is then selected dependent on one or more of the assigned grayscale values, per numeral  167 . Note again that the relationship between desired layer thickness and grayscale value need not be linear. For example, if a minimum eight-bit value of, e.g., “67” was needed to achieve a continuous film for a particular embodiment, then an assigned thickness might be represented by a number in the range of 0, 67-255. 
       FIG.  1 B  also introduces an optional (dashed-line) process,  169 , relating to the use of error correction data (or other data) to influence halftoning. This can be applied in a number of ways, but to provide one introductory example, if it is determined in practice for a particular printing mechanism that a subset of ink nozzles are inoperative, the halftone pattern can be optionally adjusted to provide compensation (e.g., the pattern can be varied, or AM halftoning can be applied instead of FM halftoning, or another scheme can be used), or the print head can be instructed to use different nozzles (e.g., with an optional offset in scan path); as such error data would presumably affect each pass of a subject-print head over the substrate, the halftoning algorithm can optionally be updated, at least for the subject-print head, to perform future printing or print planning using modified parameters. In other embodiments, drive waveforms for a particular ink nozzle can be varied or tuned. For example, process variations for each nozzle (and other factors such as nozzle life/age and ink parameters such as viscosity, surface tension and temperature) can influence per-nozzle droplet volume; to mitigate this effect, the drive waveform for the nozzle can be varied in order to adjust volume, trajectory or velocity of an ejected droplet that contributes to an assigned or desired halftone pattern. Similar corrections/updates can be supplied depending on deposition machine particulars, ink qualities, and other factors. Note that error correction can also take other forms, for example, varying droplet size or shape, or changing the spatial positioning of droplets within a print cell. Applicant’s copending PCT Patent Application No. PCT/US14/35193 for “Techniques for Print Ink Droplet Measurement and Control to Deposit Fluids within Precise Tolerances,” filed on behalf of first named inventor Nahid Harjee on Apr. 23, 2014 (KT 13-0616CP) discloses techniques for individualized droplet volume, trajectory and velocity measurement, the validation of droplets as useable or aberrant to a point where a nozzle should be excluded from use, planning of print head scan paths around such issues, and the adjustment of (and provision of alternate) nozzle drive waveforms and other compensation for use in correcting such behavior; this mentioned application is hereby incorporated by reference, as though set forth herein. Various techniques for error correction will be discussed below but, as represented by optional process  169 , if applied, such techniques can be used to adjust how an individual pattern is created, to correct for aberration in a deposited layer. Any of the techniques or processes described in the aforementioned copending PCT patent application (KT 13-0616CP) can be applied to adjust droplet generation to promote uniform droplet generation and/or error compensation. 
       FIG.  1 C  provides yet another flow diagram used to introduce the processes discussed above. A method implementing these processes is generally identified using numeral  181 . First, layer data is received ( 183 ), for example, identifying size and shape of a desired layer and thickness of the desired layer. In one embodiment, the desired layer will be a part of a completed flat panel display (e.g., a television or other display device) and, in another embodiment, the desired layer will be part of a solar panel. Optionally, in some implementations, the desired layer is an encapsulation layer that will protect active elements of such a device against oxygen and/or water. As exemplified by dashed-line box  184 , layer data can be optionally expressed in the form of a width, length and height (e.g., x microns by y microns by z microns, as depicted). Per box  185 , the thickness data (e.g., “z microns” in this example) is then optionally converted to grayscale values, one for each one of multiple print cells, according to a mapping ( 186 ). For example, if it is determined that a layer thickness of 5.0 microns (i.e., z = 5.0) corresponds to a specific ink volume, achieved by firing M droplets per some unit area, then grayscale values correlated with this ink droplet density (i.e., per mapping  186 ) are assigned to each print cell, as depicted in an example box  187 . In this hypothetical, box  187  shows a grid of values “203” which (in this example) are already known to provide the desired ink density needed to obtain a 5.0 micron thick layer following application of ink. Per numeral  189 , grayscale values or grid values can be optionally adjusted. For example, in one contemplated embodiment, grayscale values representing a border (e.g., periphery of a layer to be deposited) can be adjusted to avoid buildup at layer edges (see the discussion of  FIGS.  7 A- 7 E , below). Alternatively, if deposited ink has non-uniformities that can be linked to specific nozzles or print cells, then grayscale values can be adjusted so as to mitigate such non-uniformities. In an embodiment where the substrate has underlying structures (such that a uniform thickness of deposited ink results in a non-uniform surface because of underling active elements), then the gray scale values can be adjusted so as to level out the post-deposition surface of the new layer. Such adjustment can be applied before or after conversion of grayscale values to a halftone pattern, per process  191  (or otherwise optionally factored into the halftoning process). The halftoning process results in a bitmap where each grid intersection point is associated with a possible droplet, and where an individual grid value (e.g., single bit value) at a grid intersection point indicates whether a droplet is to be fired at the corresponding grid intersection point, as exemplified in example box  192 . The result of this process is also a set of printer control instructions, amendable for use in printing the desired layer, for storage for later download, transfer, use or manipulation, or for prospectively controlling a printer. The ultimate printing operation is designated by the numeral  193  in  FIG.  1 C . 
     With the principal parts of several embodiments thus introduced, this description will now provide additional detail relating to certain fabrication techniques.  FIGS.  2 A-D  will first be used to explain particulars of one possible deposition environment, e.g., an industrial fabrication machine that uses ink jet printing to deposit material that will directly form one or more permanent layers of a flat panel device.  FIGS.  3 A- 6 B  will then be used to explain how halftoning can be used to control to layer thickness.  FIGS.  7 A- 7 E  will be used to discuss edge buildup and boundary control.  FIGS.  8 A- 8 E  will be used to narrate a hypothetical fabrication process. Finally,  FIG.  9    will be used to discuss some fabrication options in manufacturing an OLED display device. These FIGS. and associated text should be understood to provide examples only, and other analogous techniques and implementations will no doubt occur to those skilled in the art. Using the described techniques and devices, a printing process and more specifically an ink jet printing process can be used to deposit nearly any desired layer using a fluidic ink, with uniform control over layer thickness provided by use of and adjustment of a halftone pattern. The described techniques are especially useful for “blanket” depositions, that is, where feature size of a deposited layer is large relative to any underlying nanoscale structures, but the techniques described above are not so limited. 
       FIG.  2 A  represents a number of different implementation tiers, collectively designated by reference numeral  201 ; each one of these tiers represents a possible discrete implementation of the techniques introduced herein. First, halftoning techniques as introduced in this disclosure can take the form of instructions stored on non-transitory machine-readable media, as represented by graphic  203  (e.g., executable instructions or software for controlling a computer or a printer). Second, per computer icon  205 , these techniques can also optionally be implemented as part of a computer or network, for example, within a company that designs or manufactures components for sale or use in other products. Third, as exemplified using a storage media graphic  207 , the techniques introduced earlier can take the form of a stored printer control instructions, e.g., as a halftone print image that, when acted upon, will cause a printer to fabricate one or more layers of a component dependent on the use of one or more halftone patterns representing different ink volumes, per the discussion above. Note that printer instructions can be directly transmitted to a printer, for example, over a LAN; in this context, the storage media graphic can represent (without limitation) RAM inside or accessible to a computer or printer, or a portable media such as a flash drive. Fourth, as represented by a fabrication device icon  209 , the techniques introduced above can be implemented as part of a fabrication apparatus or machine, or in the form of a printer within such an apparatus or machine. It is noted that the particular depiction of the fabrication device  209  represents one exemplary printer device that will be discussed in connection with  FIG.  2 B , below. The techniques introduced above can also be embodied as an assembly of manufactured components; in  FIG.  2 A  for example, several such components are depicted in the form of an array  211  of semi-finished flat panel devices, that will be separated and sold for incorporation into end consumer products. The depicted devices may have, for example, one or more encapsulation layers or other layers fabricated in dependence on the methods introduced above. The techniques introduced above can also be embodied in the form of end-consumer products as referenced, e.g., in the form of display screens for portable digital devices  213  (e.g., such as electronic pads or smart phones), as television display screens  215  (e.g., OLED TVs), solar panels  217 , or other types of devices. 
       FIG.  2 B  shows one contemplated multi-chambered fabrication apparatus  221  that can be used to apply techniques disclosed herein. Generally speaking, the depicted apparatus  221  includes several general modules or subsystems including a transfer module  223 , a printing module  225  and a processing module  227 . Each module maintains a controlled environment, such that printing for example can be performed by the printing module  225  in a first controlled atmosphere and other processing, for example, another deposition process such an inorganic encapsulation layer deposition or a curing process (e.g., for printed materials), can be performed in a second controlled atmosphere. The apparatus  221  uses one or more mechanical handlers to move a substrate between modules without exposing the substrate to an uncontrolled atmosphere. Within any given module, it is possible to use other substrate handling systems and/or specific devices and control systems adapted to the processing to be performed for that module. 
     Various embodiments of the transfer module  223  can include an input loadlock  229  (i.e., a chamber that provides buffering between different environments while maintaining a controlled atmosphere), a transfer chamber  231  (also having a handler for transporting a substrate), and an atmospheric buffer chamber  233 . Within the printing module  225 , it is possible to use other substrate handling mechanisms such as a flotation table for stable support of a substrate during a printing process. Additionally, a xyz-motion system, such as a split axis or gantry motion system, can be used for precise positioning of at least one print head relative to the substrate, as well as providing a y-axis conveyance system for the transport of the substrate through the printing module  225 . It is also possible within the printing chamber to use multiple inks for printing, e.g., using respective print head assemblies such that, for example, two different types of deposition processes can be performed within the printing module in a controlled atmosphere. The printing module  225  can comprise a gas enclosure  235  housing an inkjet printing system, with means for introducing an inert atmosphere (e.g., nitrogen) and otherwise controlling the atmosphere for environmental regulation (e.g., temperature and pressure), gas constituency and particulate presence. 
     Various embodiments of a processing module  227  can include, for example, a transfer chamber  236 ; this transfer chamber also has a including a handler for transporting a substrate. In addition, the processing module can also include an output loadlock  237 , a nitrogen stack buffer  239 , and a curing chamber  241 . In some applications, the curing chamber can be used to cure a monomer film into a uniform polymer film, for example, using a heat or UV radiation cure process. 
     In one application, the apparatus  221  is adapted for bulk production of liquid crystal display screens or OLED display screens, for example, the fabrication of an array of eight screens at once on a single large substrate. These screens can be used for televisions and as display screens for other forms of electronic devices. In a second application, the apparatus can be used for bulk production of solar panels in much the same manner. 
     Applied to the encapsulation example discussed above, and adapted to use the halftone-based printing techniques described above, the printing module  225  can advantageously be used in such applications to deposit organic encapsulation layers that help protect the sensitive elements of such devices. For example, the depicted apparatus  221  can be loaded with a substrate and can be controlled to move the substrate back and forth between the various chambers in a manner uninterrupted by exposure to an uncontrolled atmosphere during the encapsulation process. The substrate can be loaded via the input loadlock  229 . A handler positioned in the transfer module  223  can move the substrate from the input loadlock  229  to the printing module  225  and, following completion of a printing process, can move the substrate to the processing module  227  for cure. By repeated deposition of subsequent layers, each of controlled thickness, aggregate encapsulation can be built up to suit any desired application. Note once again that the techniques described above are not limited to encapsulation processes, and also that many different types of tools can be used. For example, the configuration of the apparatus  221  can be varied to place the various modules  223 ,  225  and  227  in different juxtaposition; also, additional, fewer or different modules can also be used. 
     While  FIG.  2 B  provides one example of a set of linked chambers or fabrication components, clearly many other possibilities exist. The halftoning techniques introduced above can be used with the device depicted in  FIG.  2 B , or indeed, to control a fabrication process performed by any other type of deposition equipment. 
       FIG.  2 C  provides a plan view of the substrate and printer as they might appear during the deposition process. The print chamber is generally designated by reference numeral  251 , the substrate to be printed upon is generally designated by numeral  253 , and a support table used to transport the substrate is generally designated by numeral  255 . Generally speaking, any x-y coordinate of the substrate is reached by a combination of movements, including x- and y-dimensional movement of the substrate by the support table (e.g., using flotation support, as denoted by numeral  257 ) and using “slow axis” x-dimensional movement of one or more print heads  259  along a traveler  261 , as generally represented by arrows  263 . As mentioned, the flotation table and substrate handling infrastructure are used to move the substrate and advantageously provide deskew control along one or more “fast axes,” as necessary. The print head is seen to have plural nozzles  265 , each of which is separately controlled by a firing pattern derived from a halftone print image (e.g., to effectuate printing of columns of print cells as the print head is moved from left-to-right and vice-versa along the “slow axis”). Note that while only 5 nozzles are depicted in  FIG.  2 C  that any number of nozzles can be used; for example, in a typical industrial printing implementation, there can be multiple print heads with thousands of nozzles present. With relative motion between the one or more print heads and the substrate provided in the direct of the fast axis (i.e., the y-axis), printing describes a swath that follows individual rows of print cells. The print head can also advantageously be adjusted to vary effective nozzle spacing (e.g., by rotating of the one or more print heads, per numeral  267 ). Note that multiple such print heads can be used together, oriented with x-dimension, y-dimension, and/or z-dimensional offset relative to one another as desired (see axis legend  269  in  FIG.  2 C ). The printing operation continues until the entire target region (and any border region) has been printed with ink, as desired. Following deposition of the necessary amount of ink, the substrate is finished, either by evaporating solvent to dry ink (e.g., using a thermal process), or by use of a cure process, such as a UV cure process. 
       FIG.  2 D  provides a block diagram showing various subsystems of one apparatus ( 271 ) that can be used to fabricate devices having one or more layers as specified herein. Coordination over the various subsystems is provided by a processor  273 , acting under instructions provided by software (not shown in  FIG.  2 D ). During a fabrication process, the processor feeds data to a print head  275  to cause the print head to eject various volume of ink depending on firing instructions provided by a halftone print image. The print head  275  typically has multiple ink jet nozzles, arranged in a row or array, and associated reservoirs that permit jetting of ink responsive to activation of piezoelectric or other transducers; such transducers cause a respective nozzle to eject a controlled amount of ink in an amount governed by an electronic firing waveform signal applied to the corresponding piezoelectric transducer. Other firing mechanisms can also be used. The print head applies the ink to a substrate  277  at various x-y positions corresponding to the grid coordinates within various print cells, as represented by the halftone print image. Variation in position is effected both by a print head motion system  279  and substrate handling system  281  (e.g., that cause the printing to describe one or more swaths across the substrate). In one embodiment, the print head motion system  279  moves the print head back-and-forth along a traveler, while the substrate handling system provides stable substrate support and both “x” and “y” dimension transport (and rotation) of the substrate, e.g., for alignment and deskew; during printing, the substrate handling system provides relatively fast transport in one dimension (e.g., the “y” dimension relative to  FIG.  2 C ), while the print head motion system  279  provides relatively slow transport in another dimension (e.g., the “x” dimension relative to  FIG.  2 C ), e.g., for print head offset. In another embodiment, multiple print heads can be used, with primary transport being handled by the substrate handling system  281 . An image capture device  283  can be used to locate any fiducials and assist with alignment and/or error detection. 
     The apparatus also comprises an ink delivery system  285  and a print head maintenance system  287  to assist with the printing operation. The print head can be periodically calibrated or subjected to a maintenance process; to this end, during a maintenance sequence, the print head maintenance system  287  is used to perform appropriate priming, purge of ink or gas, testing and calibration, and other operations, as appropriate to the particular process. Such a process can also include individual measurement of parameters such as droplet volume, velocity and trajectory, for example, as discussed in Applicant’s copending PCT patent application referenced earlier (KAT-13-616CP), and as referenced by numerals  291  and  292 . 
     As was introduced previously, the printing process can be performed in a controlled environment, that is, in a manner that presents a reduced risk of contaminants that might degrade effectiveness of a deposited layer. To this effect, the apparatus includes a chamber control subsystem  289  that controls atmosphere within the chamber, as denoted by function block  290 . Optional process variations, as mentioned, can include performing jetting of deposition material in presence of an ambient nitrogen gas atmosphere (or another inert environment, having a specifically selected gas and/or controlled to exclude unwanted particulate). Finally, as denoted by numeral  293 , the apparatus also includes a memory subsystem that can be used to store halftone pattern information or halftone pattern generation software, i.e., should the apparatus directly perform rendering of layout data to obtain a halftone print image according to the techniques introduced above, to internally generate printer control instructions that govern the firing of (and timing of) each droplet. If such rendering is performed elsewhere, and the task of the apparatus is to fabricate a device layer according to a received printer instructions, then the halftone print image can be stored in the memory subsystem  293  for use during the printing process. As noted by numeral  294 , in one optional embodiment, individual droplet particulars can be varied (e.g., to correct for nozzle aberration) through the variation of firing waveform for any given nozzle. In one embodiment, a set of alternate firing waveforms can be selected in advance and made available to each nozzle, on a shared or dedicated basis. In another embodiment, a single waveform is decided upon in advance (e.g., selected relative to alternatives) and is programmed for indefinite use in connection with a specific nozzle. 
     Structure and techniques for modifying or tuning nozzle firing particulars are explained with reference to  FIGS.  3 A- 3 C . In one embodiment, waveforms can be predefined as a sequence of discrete signal levels, e.g., defined by digital data, with a drive waveform being generated by a digital-to-analog converter (DAC). Numeral  301  in  FIG.  3 A  identifies a graph of a waveform  303  having discrete signal levels,  304 ,  305 ,  306 ,  307 ,  308 ,  309  and  310 . In one embodiment, each nozzle driver can include circuitry that receives multiple waveforms (e.g., up to sixteen or another number), with each waveform being defined as a series of signal levels of variable voltage and duration. Each waveform can be expressed as a sequence of up to sixteen such signal levels, each expressed as a multi-bit voltage and a multi-bit duration. That is to say, in such an embodiment, pulse width can effectively be varied by defining different durations for one or more signal levels, and drive voltage can be waveform-shaped in a manner chosen to provide subtle droplet size, velocity or trajectory variation, e.g., with droplet volumes gauged to provide specific volume gradations increments such as in units of 0.01 pL. Thus, with such an embodiment, waveform shaping provides ability to tailor droplet volumes and flight parameters to be close to ideal values. These waveform shaping techniques also facilitate a strategy for reducing or eliminating Mura; for example, in one optional embodiment, a single assigned nozzle drive waveform is tailored in advance for each nozzle, such that all nozzles provide uniform droplet volume (e.g., as near as possible to 10.00 pL). In another embodiment, alternative predetermined waveforms are optionally made available to each nozzle, with dynamic calibration (or another process) used to select (e.g., program) “the one” of the alternative predetermined waveforms that is to be applied in the short term. Other possibilities also exist. 
     Typically, the effects of different drive waveforms and resultant droplet volumes are measured in advance. In one embodiment, for each nozzle, up to sixteen different drive waveforms can be stored in a nozzle-specific, dedicated, 1k static random access memory (SRAM) for later, elective use in providing discrete volume variations, as selected by software. With the different drive waveforms on hand, each nozzle is then instructed droplet-by-droplet as to which waveform to apply via the programming of data that effectuates the specific drive waveform. 
       FIG.  3 B  is a diagram showing circuitry that can be used to such an embodiment, generally designated by numeral  321 . In particular, a processor  323  is used to receive data defining a particular layer of material that is to be printed. As represented by numeral  325 , this data can be a layout file or bitmap file that defines desired thickness per grid point or positional address. A series of piezoelectric transducers  327 ,  328  and  329  generate associated respective droplet volumes  331 ,  332  and  333 , that are each dependent on many factors, including nozzle drive waveform, nozzle-to-nozzle and print-head-to-print-head manufacturing variations. During a calibration operation, each one of a set of variables can be tested for its effects on droplet volume, including nozzle-to-nozzle variation, to determine one or more drive waveforms for the respective nozzle, given the particular ink that will be used; if desired, this calibration operation can be made dynamic, for example, to respond to changes in temperature, nozzle clogging, print head age or other parameters. This calibration is represented by a droplet measurement device  335 , which provides measured data to the processor  323  for use in managing print planning and ensuing printing. In one embodiment, this measurement data is calculated during an operation that takes minutes, e.g., no more than thirty minutes for thousands of nozzles and preferably much less time (e.g., for thousands of print head nozzles and potentially, for each nozzle, dozens of possible nozzle firing waveforms). In another embodiment, such measurement can be performed iteratively, that is to update different subsets of nozzles at different points in time. A non-imaging (e.g., interferometric) technique can optionally be used for measurement, for example, as described in the aforementioned copending, commonly-assigned PCT patent application; this potentially results in dozens of droplet measurements per nozzle, covering dozens to hundreds of nozzles per second. This data and any associated statistical models (and means) can be stored in memory  337  for use in processing the layout or bitmap data  325  when it is received. In one implementation, processor  323  is part of a computer that is remote from the actual printer, whereas in a second implementation, processor  323  is either integrated with a fabrication mechanism (e.g., a system for fabricating displays) or with a printer. 
     To perform the firing of droplets, a set of one or more timing or synchronization signals  339  are received for use as references, and these are passed through a clock tree  341  for distribution to each nozzle driver  343 ,  344  and  345  to generate the drive waveform for the particular piezoelectric transducer ( 327 ,  328  and  329 , respectively), i.e., with a dedicated piezoelectric transducer per nozzle (and with thousands of nozzles typically present, even though only three are illustrated in  FIG.  3 B ). Each nozzle driver has one or more registers  351 ,  352  and  353 , respectively, which receive multi-bit programming data and timing information from the processor  323 . Each nozzle driver and its associated registers receive one or more dedicated write enable signals (we n ) for purposes of programming the registers  351 ,  352  and  353 , respectively. In one embodiment, each of the registers comprises a fair amount of memory, including a 1 k SRAM to store multiple, predetermined waveforms, and programmable registers to select between those waveforms and otherwise control waveform generation. The data and timing information from the processor is depicted in  FIG.  3 B  as multi-bit information, although this information can instead be provided via a serial connection to each nozzle (as will be seen in  FIG.  3 C , discussed below). 
     For a given deposition, print head or ink, the processor chooses for each nozzle a set of sixteen prearranged drive waveforms that can be electively (i.e., “at will”) applied to generate a droplet; note that this number is arbitrary, e.g., in one design, four waveforms could be used, while in another, four thousand could be used. These waveforms are advantageously selected to provide desired variation in output droplet volume for each nozzle, e.g., to cause each nozzle to have at least one waveform choice that produces a near-ideal droplet volume (e.g., a mean droplet volume of 10.00 pL) and to accommodate a range of deliberate volume variation for each nozzle that can be used to produce an ideal droplet size, ejection velocity and flight trajectory. In various embodiments, the same set of sixteen drive waveforms are used for all of the nozzles, though in the depicted embodiment, sixteen, possibly-unique waveforms are each separately defined in advance for each nozzle, each waveform conferring respective droplet volume (and velocity and trajectory) characteristics. 
     During printing, to control deposition of each droplet, data selecting one of the predefined waveforms is then programmed into each nozzle’s respective registers  351 ,  352  or  353  on a nozzle-by-nozzle basis. For example, given a target droplet volume of 10.00 pL, nozzle driver  343  can be configured through writing of data into registers  351  to set one of sixteen waveforms corresponding to one of sixteen different droplet volumes. The volume produced by each nozzle would have been measured by the droplet measurement device  335 , with nozzle-by-nozzle (and waveform-by-waveform) droplet volumes and associated distributions registered by the processor  323  and stored in memory. The processor can, by programming the register  351 , define whether or not it wants the specific nozzle driver  343  to output a processor-selected one of the sixteen waveforms. In addition, the processor can program the register to have a per-nozzle delay or offset to the firing of the nozzle for a given scan line (e.g., to optionally correct for substrate skew, to correct for error including velocity or trajectory error, and for other purposes); this offset is effectuated by counters which delay firing of the particular nozzle by a programmable number of timing pulses for each scan. To provide an example, if the result of droplet measurement indicates that one particular nozzle’s droplet tends to have a lower than expected velocity, then the corresponding nozzle waveform can be triggered earlier (e.g., advanced in time, by reducing a dead time preceding the active signal levels used for piezoelectric actuation); conversely, if the result of droplet measurement indicates that the one particular nozzle’s droplet has a relatively high velocity, then the waveform can be triggered later, and so forth. Other examples are clearly possible - for example, a slow droplet velocity can be counteracted in some embodiments by increasing drive strength (i.e., signal levels and associated voltage used to drive a given nozzle’s piezoelectric actuator). In one embodiment, a sync signal distributed to all nozzles occurs at a defined interval of time (e.g., one microsecond) for purposes of synchronization and in another embodiment, the sync signal is adjusted relative to printer motion and substrate geography, e.g., to fire every micron of incremental relative motion between print head and substrate. The high speed clock (φ hs ) is run thousands of times faster than the sync signal, e.g., at 100 megahertz, 33 megahertz, etc.; in one embodiment, multiple different clocks or other timing signals (e.g., strobe signals) can be used in combination. The processor also optionally programs values defining or adjusting print grid spacing (or equivalently, timing); in one implementation, the print grid spacing is common to the entire pool of available nozzles and is equal to the halftone grid spacing, though this need not be the case for each implementation. For example, in some cases, a printer grid can be defined in a manner that adjusts timing (e.g. phase) of each nozzle’s droplet patterns so as to compensate for substrate skew or other factors. Thus, in one optional embodiment, nozzle firing patterns can be varied to effectively transform the halftone grid to match a substrate geography that is a priori unknown (e.g., with software rotating or adjusting the printer instructions as necessary for proper printing). Clearly, many design alternatives are possible. Note that the processor  323  in the depicted embodiment can also dynamically reprogram the register of each nozzle during operation, i.e., the sync pulse is applied as a trigger to launch any programmed waveform pulse set in its registers; if new data is asynchronously received by the depicted circuitry before the next sync pulse (e.g., to adjust a droplet waveform and potentially droplet timing, trajectory and/or volume), then the new data will be applied with the next sync pulse. The processor  323  also controls initiation and speed of scanning ( 355 ) in addition to setting parameters for the sync pulse generation ( 356 ). In addition, the processor controls optional rotation of the print head ( 357 ), for the various purposes described above. In this way, each nozzle can concurrently (or simultaneously) fire using any one of sixteen different waveforms for each nozzle at any time (i.e., with any “next” sync pulse), and the selected firing waveform can be switched with any other of the sixteen different waveforms dynamically, in between fires, during a single scan. 
       FIG.  3 C  shows additional detail of circuitry ( 361 ) that can be used in such an embodiment to generate output nozzle drive waveforms for each nozzle; the output waveform is represented as “nzzl-drv. wvfm” in  FIG.  3 C . More specifically, the circuitry  361  receives inputs of the sync signal, a single-ended or differential line carrying serial data (“data”), a dedicated write enable signal (we) and the high speed clock (φ hs ). A register file  363  provides data for at least three registers, respectively conveying an initial offset, a grid definition value and a drive waveform ID. The initial offset is a programmable value that adjusts each nozzle to align with the start of a print grid. For example, given implementation variables such as multiple print heads, multiple rows of nozzles, different print head rotations, nozzle firing velocity and patterns and other factors, the initial offset can be used to align each nozzle’s droplet pattern with the start of the print grid, to account for delays, skew and other factors. Offsets can be differently applied across multiple nozzles, for example, to rotate a grid or halftone pattern relative to substrate geography, or to correct for substrate misalignment; advantageously, these functions can be performed by software, i.e., by instructions stored on non-transitory, machine-readable media. Similarly, offsets can also be used to correct for aberrant velocity or other effects. The grid definition value is a number that represents the number of sync pulses “counted” before the programmed waveform is triggered (e.g., representing a firing frequency); in the case of an implementation that prints flat panel displays (e.g., OLED panels), the halftone grid firing points presumably have one or more regular spacings relative to the different print head nozzles, corresponding to a regular (constant spacing) or irregular (multiple spacing) grid. Thus, if the grid spacing value was set to two (e.g., every two microns), then each nozzle could be fired at this interval. The drive waveform ID represents a selection of one of the pre-stored drive waveforms for each nozzle, and can be programmed and stored in many manners, depending on embodiment. In one embodiment, the drive waveform ID is a four bit selection value, and each nozzle has its own, dedicated 1 k-byte SRAM to store up to sixteen predetermined nozzle drive waveforms, stored as 16x16x4B entries. Briefly, each of sixteen entries for each waveform contains four bytes representing a programmable signal level, with these four bytes representing a two-byte resolution voltage level and a two-byte programmable duration, used to count a number of pulses of the high-speed clock. Each programmable waveform can thus consist of zero to up to sixteen discrete pulses each of programmable voltage and duration (e.g., of duration equal to 0-255 pulses of a 33 megahertz clock). 
     Numerals  365 ,  366  and  367  designate one embodiment of circuitry that shows how a specified waveform can be generated for a given nozzle. A first counter  365  receives the sync pulse, to initiate a countdown of the initial offset, triggered by start of a new line scan; the first counter  365  counts down in micron increments and, when zero is reached, a trigger signal is output from the first counter  365  to a second counter  366 . This trigger signal essentially starts the firing process for each nozzle for each scan line. The second counter  366  then implements a programmable grid spacing in increments of microns. The first counter  365  is reset in conjunction with a new scan line, whereas the second counter  366  is reset using the next edge of the high-speed clock following its output trigger. The second counter  366 , when triggered, activates a waveform circuit generator  367 , which generates the selected drive waveform shape for the particular nozzle. As denoted by dashed line boxes  368 - 370 , seen beneath the generator circuit, this latter circuit is based on a high speed digital-to-analog converter  368 , a counter  369 , and a high-voltage amplifier  370 , timed according to the high-speed clock (φ hs ). As the trigger from the second counter  366  is received, the waveform generator circuit retrieves the number pairs (signal level and duration) represented by the drive waveform ID value and generates a given analog output voltage according to the signal level value, with the counter  369  effective to hold DAC output for a duration according to the counter. The pertinent output voltage level is then applied to the high-voltage amplifier  370  and is output as the nozzle-drive waveform. The next number pair is then latched out from registers  363  to define the next signal level value/duration, and so forth. 
     The depicted circuitry provides an effective means of defining any desired waveform according to data provided by the processor  323  from  FIG.  3 B . Software receives print instructions and adjusts or interacts with those instructions as necessary in order to comply with or correct for grid geometry or a nozzle with aberrant velocity or flight angle. The durations and/or voltage levels associated with any specific signal level (including a first, “delay” signal level of zero volts, which effectively defines an offset relative to sync) can be adjusted to this end. As noted, in one embodiment, the processor decides upon a set of waveforms in advance (e.g., sixteen possible waveforms, per-nozzle) and it then writes definition for each of these selected waveforms into SRAM for each nozzle’s driver circuitry, with a “firing-time” decision of programmable waveform then being effected by writing a four-bit drive waveform ID into each nozzle’s registers. 
     With optional circuitry for generating individual droplets (i.e., per nozzle droplets) thus described, this disclosure will now further discuss halftone generation techniques and associated error correction techniques. As should be appreciated, precise controls over per-nozzle droplet volume, for example, with a well formed understanding of per-nozzle droplet mean volume (and expected volume distribution) and a similar understanding for droplet flight and trajectory, and with optional circuitry for varying per-nozzle waveforms, droplet timing, droplet volume and other particulars, permits deposition of very precise ink droplets using the techniques described above. 
       FIG.  4 A  provides a method diagram  401  for controlling layer thickness using halftoning. These techniques can optionally be used with the waveform tuning techniques and circuitry described above. More specifically, as depicted by numeral  403 , layout data  403  is first received and used to define the desired grid ( 405 ). This grid will bear a relationship to nozzle spacing used by the printer ( 407 ) and, accordingly, software determines this relationship and uses this relationship to plan halftoning and print parameters such as scan path, to develop printer control instructions. Software also receives ink volume data ( 409 ), which for example, identifies the amount of ink per unit area needed to achieve a desired layer thickness. Note that in one embodiment, the correlation between volume and thickness is measured after test layer formation (e.g., after cure or drying). In a variation, the correlation is measured on the basis of thickness of wet ink following one or more print head passes. In one embodiment, software then maps droplet density to grid pitch ( 411 ), for example, using the formula 
     
       
         
           
             Desired 
               
             Thickness=h 
             × 
             
               
                 
                   
                     
                       
                         Volume 
                       
                       
                         drop 
                       
                     
                   
                   
                     
                       
                         Pitch 
                       
                       
                         in-scan 
                       
                     
                     × 
                     
                       
                         Pitch 
                       
                       
                         cross-scan 
                       
                     
                   
                 
               
             
           
         
       
     
      as also seen within dashed-line box  412 . The in-scan pitch represents the spacing between drop opportunities in a first direction of relative motion between the print head and substrate, the cross-scan pitch represents the spacing between drop opportunities in a direction generally perpendicular to (or otherwise independent of) this first direction, and the parameter h (times 100) is the grayscale value in percentage. In one embodiment, this relationship can vary over time and, thus, can be re-measured to develop empirical data ( 413 ), for dynamic factors such as process or temperature, for specific machine or ink particulars, for nozzle age, or for other factors. 
     With desired droplet density identified, software then invokes a halftone pattern generation subroutine (or a separate software planning process), as represented by numeral  415 . In one embodiment, this planning can be performed by a remote computer while, in another embodiment, this process is integrated with the printer. The halftone pattern generation function plans droplet deposition patterns so as to produce droplet patterns, with each droplet having substantially uniform volume, according to a selection of points on a halftone grid. In another embodiment, droplet variation is not necessarily uniform, but rather, droplet measurements are factored into halftone pattern generation, i.e., such that selected gridpoints for droplet firings contemplate specific droplet volumes (or trajectories or velocities) associated with nozzles firing at those points, with the halftoning generation accommodating (and factoring in) nozzle-to-nozzle variation. Ideally, the pattern is defined so that the spreading of ink produces a locally continuous layer of material of homogeneous thickness. Planned as a single process covering the area of the entire layer (to be deposited on the substrate), and according to a single halftone grid that spans the deposition area of interest, the ink is deposited ideally in a manner that is seamless ( 416 ), i.e., to avoid Mura. As mentioned earlier, in one embodiment, desired layer thickness is apportioned to different “print cells” with a thickness or grayscale value applied to each print cell, and with the halftone generation software receiving a grayscale image (i.e., an array of grayscale values) and developing a halftone pattern based on this grayscale image (e.g., with local ink volume variation controlled by individual print cell values and with error diffusion relied upon as appropriate to achieve desired homogeneity). As noted, in another embodiment, halftone patterns can be separately (independently) planned for each of plural “tiles” of adjacent deposition areas ( 417 ) with halftone droplet patterns for each tile planned, but with halftoning performed in a complementary manner ( 418 ), such that droplet patterns are “stitched together” on a common grid, once again to avoid Mura. This is discussed below in connection with  FIG.  5 D . Note that seamless pattern interface (e.g., “stitching”) can be enhanced through the use of a continuous grid ( 420 ). In such an embodiment, groups of one or more print cells (e.g., “m” print cells) can be equated to groups of one or more tiles (e.g., “n” tiles) and used to generate a halftone pattern for each tile, per process  419 . 
       FIG.  4 B  provides another flow diagram  421  associated with these processes. As with the earlier examples, data representing layout of a desired layer is first received, per numeral  423 . This data specifies boundaries of the layer to be deposited and provides information sufficient to define thickness throughout the layer. This data can be generated on the same machine or device on which the process  421  is performed, or it can be generated by a different machine. In one embodiment, the received data is defined according to an x-y coordinate system and the provided information is sufficient to compute desired layer thickness at any represented x-y coordinate point, for example, optionally specifying a single height or thickness to be applied throughout the layer, consistent with the x-micron by y-micron by z-micron example introduced earlier. Per numeral  425 , this data can be converted to a grayscale value for each print cell in a deposition area that will receive the layer. If print cell area does not inherently correspond to the x-y coordinate system matching the layout data, then the layout data is converted (e.g., by averaging thickness data for multiple coordinate points and/or using interpolation) to obtain a grayscale value for each print cell. This conversion can be based on predetermined mapping information, for example, produced using relationships or equations such as those discussed above. Per numeral  427 , correction can optionally be performed at this stage upon the grayscale values in order to ultimately produce a homogeneous layer (or for other desired effect). To provide one example (which will be discussed further below), if it is desired to compensate for varying heights of microstructures that will sit underneath the desired layer, an optional technique adds offsets to select grayscale values to “boost” the layer of interest at specific locations to effectively planarize a top surface of the deposited layer; for example, a desired 5.0 micron thick encapsulation layer is desired across a deposition region, and structures defining the underlying substrate vary by e.g., a micron in thickness, then grayscale values could be manipulated to deposit 6.0 micron thick encapsulation in some areas, in an effort to produce a level top surface of the encapsulation layer. Other techniques are also possible. In one embodiment, such grayscale value manipulation can also be used to correct for nozzle firing aberration (e.g., in the in-scan direction) to deposit more ink (for example, if a particular nozzle or set of nozzles produce insufficient ink volume) or less ink (e.g., the particular nozzle or set of nozzles produce excess ink volume). Such an optional process can be predicated on a calibration process and/or empirically-determined data, per function block  434 . The grayscale values are then converted to a halftone pattern, per numeral  429 , with error diffusion across the halftone grid relied upon to help ensure localized layer homogeneity. Based on this halftoning process, a print image (or other printer control instructions) is then generated, per numeral  430 . 
       FIG.  4 B  also shows use of a number of optional error correction processes  433 , applied to help ensure uniformity in the deposited layer. Such uniformity can be important to device quality, whether to ensure development of adequate encapsulation to produce a water/oxygen barrier, or to provide high-quality light generating or light guiding elements of a display panel, or for other purpose or effect. As noted above, a calibration process or empirically determined (dead-reckoned) data can be used to correct grayscale values attributable to nozzle droplet variation or other factors, per numeral  434 . Alternatively, individual nozzle drive waveforms can be planned or adjusted to correct error, as represented by numeral  435 . In yet another embodiment, nozzles can be validated or qualified ( 439 ), with each nozzle either determined to meet minimum droplet generation thresholds or disqualified from use. If a specific nozzle is disqualified, then in order to generate the desired halftone pattern, a different nozzle (or repeated pass of acceptable nozzles) can be used to deposit the droplet(s) that would otherwise have been printed by the disqualified nozzle, per numeral  436 . For example, in one embodiment, a print head has nozzles arranged both in rows and columns, such that if one nozzle is aberrant, a different, redundant nozzle can be used to deposit the droplet desired for a particular grid point. Optionally also, such issues can be taken into account and used to adjust a scan path, for example, offsetting the print head in a manner such that the desired droplet(s) can be deposited using a different nozzle (with the print head adjusted in position so as to permit this). This is represented by the numeral  437  in  FIG.  4 B . Alternatively, an error can be generated ( 438 ) and used to prompt software to select a different halftone pattern (e.g., that relies on a different nozzle). Many such alternatives are possible. As represented by numerals  440  and  441 , in one embodiment, each nozzle is calibrated in advance using a droplet measurement device ( 440 ) that repeatedly measures droplet parameters (to develop a per-nozzle or per-drive waveform distribution of measurements), with software then building a statistical model ( 441 ) for each nozzle with an understanding of nozzle droplet means for volume, velocity and trajectory, and with an understanding of expected per-nozzle variance for each of these parameters. This data can be used to qualify/validate specific nozzles (and/or droplets), as mentioned, or to select nozzles or nozzle waveforms that will be used to produce each individual droplet. Each such measurement/error correction process can be factored into print planning ( 431 ), including scan path planning, i.e., such that printer data (or print control instructions) are generated and/or updated so as to optimize the print process, while ensuring desired layer properties. Finally, per numeral  445 , final printer data (e.g., a final print image or other printer control instructions) is then generated for sending to the printer at fabrication time. 
     As noted, in order to assess the need for error correction, a calibration process can be performed specific to the ink, machine and process that will be used to form the desired layer of material. In one embodiment, therefore, techniques introduced herein can be applied to test droplet and/or halftone parameters and to provide inputs that ultimately affect the halftone pattern or final print image. For example, such calibration can be used to gauge grayscale values (e.g., in order to determine which grayscale values to apply to particular desired thicknesses) or to calibrate halftone generation so that generated halftone patterns reliably map assigned grayscale values to the desired thicknesses. Other alternatives are also possible. Exemplary techniques based on patterns are generally designated by numeral  451  in  FIG.  4 C , while exemplary techniques based on individual droplet measurement and nozzle qualification are explained in reference to  FIG.  4 D . 
     As part of the calibration process, a halftone pattern (or associated halftoning parameters) can be assigned to thickness data ( 452 ) to generate a print image  453  representing a layer. The layer can be part of a test run, for example, selected to provide uniform layer thickness atop a flat substrate, but alternatively, can be data correlated in advance with expected results. In one embodiment, the data can represent a standard applied in a “live” print process or product run. As before, the print image is formed by translating desired layer thickness for each of plural print cells into associated grayscale values (i.e., with a grayscale value for each print cell). Each per-print cell grayscale value is used to select a halftone pattern. In this embodiment also, the halftone pattern is optionally selected to produce a macroscopically-continuous film (e.g., so as to produce a layer impervious or resistant to penetration by water or oxygen). As represented by alternate flow paths  455  and  457 , the halftone print image can be used either to control a printer in an actual deposition process or can be applied to a simulation process (i.e., by a software program) to simulate/estimate qualities of the finished layers, given any other pertinent process parameters (e.g., dot gain for a particular ink formulation, measured droplet volumes and so forth). For example, with a test deposition, a resultant device could be measured with a stylus profilometer, optical interferometer or camera, with the results used to assess layer quality. See, e.g., the discussion of  FIGS.  7 A and  7 D  below. Any results are then analyzed, per numeral  459 , to assess uniformity and presence of defects, holes or voids. More generally, the results are compared by an error process ( 461 ) with expected results ( 462 ) to determine deviation. For example, a fabricated or simulated layer may be thinner in some areas than in other areas which, if a uniformly flat layer was expected, might represent a failure in the nozzle firing pattern. The error process  461  detects such deviations and correlates deviations with specific types of errors. If no deviation is detected, and the layer has exactly the correct thickness, the process tentatively associates the selected grayscale values with a specific thickness and updates stored data or other settings, as appropriate, per numerals  463  and  465 . Note that this association can later be adjusted/updated as necessary, via another loop or pass of the configuration method  451 . The method  451  can then be repeated ( 466 ) for other desired layer thicknesses and/or gradients, in order to fully develop a comprehensive mapping between different selectable grayscale values and desired thicknesses. Per numeral  467 , if deviation between the simulated or physical layer and the expected data is detected, associated process parameters are responsively adjusted. As reflected by numerals  468 - 472 , some of the parameters that can be adjusted include selected grayscale values (e.g., the relation of grayscale values to thicknesses is changed if the test layer is too thick or thin), factors influencing dot gain (e.g., ink viscosity, surface tension or other factors) or drop coverage (e.g., droplet shape, size, driver waveform, etc.), grid spacing or mapping, or any other desired parameters. The process can incrementally adjust (e.g., increment or decrement) each setting, store updated adjustment data ( 473 ) as appropriate, and optionally repeat the method  451  to test the new settings. Once any adjusted settings are determined to be correct (i.e., when error process  461  detects no error), the settings and any adjustment data are stored per reference numeral  465 . Note that in some applications (not necessarily all), scaling of grayscale values to desired thicknesses will be linear, such that this calibration process can be performed using only a small number (e.g., 2) of data points. Once this process is complete, a complete mapping should be available that links each permissible grayscale value to a specific layer thickness. At this point, the method ends. Note that the method  451  can be performed multiple times, e.g., to obtain halftone patterns to be applied for each of multiple specific machines or print heads, for use in general across plural machines or print heads, for each different types of ink or layer materials, or to customize process to any variable affecting the deposition process. 
     In some applications, it might be desired to deposit a layer of material over underlying structures, such as electric pathways, transistors and other devices. This might be the case where the desired application is solar panel or OLED fabrication, as non-limiting examples, and where the material layer is to “blanket” these structures. For example, the techniques discussed above can be applied to deposit one or more organic barrier or encapsulation layers, e.g., as part of an encapsulation layer stack that includes alternating organic/inorganic barrier layer pairs. In such an instance, it might be desired to have such encapsulation result in a relatively flat post deposition surface, notwithstanding varying topography created by underlying structures. To this effect, the method  451  can also be optionally performed for a given design, as represented by process block  475 , to develop print cell-level (e.g., grayscale value) correction data that will be used to adjust the thickness of the encapsulation layer on a print cell-by-print cell basis to adjust jetted ink to account for variation in the height of underlying structures. Such correction data is optionally used to develop a correction image that can be used to adjust desired layer thickness for a particular design or, alternatively, to update/overwrite original thickness data by modifying grayscale values pre-deposition or by performing a second deposition. As an alternative, in many embodiments, a smoothing or barrier layer can also be deposited prior to encapsulation using conventional techniques, so as to effectively planarize the substrate prior to receiving the layer of interest. For example, a deposition process can be used to “fill in” and effectively planarize top surface layers of the substrate and, subsequently, encapsulation can be added using the printing process and related data conversions discussed herein. In yet another variation, in one error process, if it is determined that certain nozzle sets or grayscale values produce volumes that are off target, the original grayscale values can be adjusted at the level of the grayscale print image to correct for this error also. In another embodiment, corrections can be applied at the bitmap (i.e., print image) level. These processes are generally represented in  FIG.  4 C  via the application of a substrate-level “map” or set of correction values, e.g., to planarize any deviation in a surface of a deposited layer. Whatever the motivation, numeral  475  represents that a correction can be applied, either to instructions for depositing ink, or via an additional post deposition process, to adjust (i.e., to normalize) data so as to obtain layer homogeneity. 
       FIG.  4 D  provides a flow diagram  481  relating to droplet measurement and nozzle qualification. In one embodiment, droplet measurement is performed within a printer using a droplet measurement device to obtain statistical models (e.g., distribution and mean) for each nozzle and for each waveform applied to any given nozzle, for each of droplet volume, velocity and trajectory. That is, as noted earlier, droplet volume and other droplet parameters can vary, not only-nozzle-to-nozzle, but over time, with each droplet varying according to statistical parameters. Thus, in order to model droplets and account for statistical variation, repeated measurements are taken and used to develop an understanding of a mean (µ) and standard deviation (σ) for each of these parameters for each nozzle. For example, during a calibration operation (or maintenance operation), a number of measurements (e.g., 6, 12, 18, or 24 measurements) can be taken of droplets from a given nozzle and used to obtain a reliable indicator of droplet expected volume, velocity and trajectory. Such measurements can optionally be dynamically performed, e.g., every hour, day or on another intermittent or periodic process. Note that as referenced above, some embodiments can assign different waveforms for use in generating droplets of slightly different parameters from each nozzle (see  FIGS.  3 A- 3 C , discussed above). Thus, for example, if there are three choices of waveforms for each of a dozen nozzles, there are up to 36 waveform-nozzle combinations or pairings, or 36 different sets of expected droplet characteristics that can be obtained from the given set of nozzles; in one embodiment, measurements are taken for each parameter for each waveform-nozzle pairing, sufficient to develop robust statistical model for each pairing and sufficient to have a high-confidence, narrow distribution of droplet values. Note that, despite planning, it is conceptually possible that a given nozzle or nozzle-waveform pairing may yield an exceptionally wide distribution, or a mean which is sufficiently aberrant that it should be specially treated. Such treatment applied in one embodiment is represented conceptually by  FIG.  4 D . 
     More particularly, a general method is denoted using reference numeral  481 . Data stored by the droplet measurement device  483  is stored in memory  484  for later use. During the application of method  481 , this data can be recalled from memory and data for each nozzle or nozzle-waveform pairing can be extracted and individually processed ( 485 ). In one embodiment, a normal random distribution is built for each variable, described by a mean, standard deviation and number of droplets measured (n), or using equivalent measures. Note that other distribution formats (e.g., Student’s-T, Poisson, etc.), can be used. Measured parameters are compared to one or more ranges ( 487 ) to determine whether the pertinent droplet can be used in practice. In one embodiment, at least one range is applied to disqualify droplets from use (e.g., if the droplet has a sufficiently large or small volume relative to desired target, then that nozzle or nozzle-waveform pairing can be excluded from short-term use). To provide an example, if 10.00 pL droplets are desired or expected, then a nozzle or nozzle-waveform linked to a droplet mean more than, e.g., 1.5% away from this target (e.g., &lt;9.85 pL or &gt;10.15 pL) can be excluded from use. Range, standard deviation, variance, or another spread measure can also or instead be used. For example, if it is desired to have droplet statistical models with a narrow distribution (e.g., 3σ&lt;±0.5% of mean), then droplets from a particular nozzle or nozzle-waveform pairing with measurements not meeting this criteria can be excluded. It is also possible to use a sophisticated/complex set of criteria which considers multiple factors. For example, an aberrant mean combined with a very narrow distribution might be okay, e.g., if it is desired to use droplets with 3σ volume within 10.00 pL ±0.1 pL, then a nozzle-waveform pairing producing a 9.96 pL mean with ±0.08 pL 3 σ value might be excluded, but a nozzle-waveform pairing producing a 9.93 pL mean with ±0.03 pL 3σ value might be acceptable. Clearly there are many possibilities according to any desired rejection/aberration criteria ( 489 ). Note that this same type of processing can be applied for per-droplet flight angle and velocity, i.e., it is expected that flight angle and velocity per nozzle-waveform pairing will exhibit statistical distribution and, depending on measurements and statistical models derived from the droplet measurement device, some droplets can be excluded. For example, a droplet having a mean velocity or flight trajectory that is outside of 5% of normal, or a variance in velocity outside of a specific target, could hypothetically be excluded from use. Different ranges and/or evaluation criteria can be applied to each droplet parameter measured and provided by storage  484 . 
     Depending on the rejection/aberration criteria  489 , droplets (and nozzle-waveform combinations) can be processed and/or treated in different manners. For example, a particular droplet not meeting a desired norm can be rejected ( 491 ), as mentioned. Alternatively, it is possible to selectively perform additional measurements ( 492 ) for the next measurement iteration of the particular nozzle-waveform pairing; as an example, if a statistical distribution is too wide as a function of measurement error, it is possible to take additional measurements for the particular nozzle-waveform, so as to improve confidence of averaged values (e.g., variance and standard deviation are dependent on the number of measured data points). Per numeral  493 , it is also possible to adjust a nozzle drive waveform, for example, to use a higher or lower voltage level (e.g., to provide greater or lesser velocity or more consistent flight angle), or to reshape a waveform so as to produce an adjusted nozzle-waveform pairing that meets specified norms. Per numeral  494 , timing of the waveform can also be adjusted (e.g., to compensate for aberrant mean velocity or droplet volume associated with a particular nozzle-waveform pairing). As an example, as noted earlier, a slow droplet can be fired at an earlier time relative to other nozzles, and a fast droplet can be fired later in time to compensate for faster flight time. Many such alternatives are possible. Per numeral  496 , any adjusted parameters (e.g., firing time, waveform voltage level or shape) can be stored for use during print scan planning. Optionally, if desired, the adjusted parameters can be applied to remeasure (e.g., validate) one or more associated droplets. After each nozzle-waveform pairing (modified or otherwise) is qualified (passed or rejected), the method then proceeds to the next nozzle-waveform pairing, per numeral  497 . 
       FIG.  5 A  shows a first example  509  of a halftone pattern and an associated, hypothetical grid. In  FIG.  5 A , the grid is seen to have five vertically-separated or “y” coordinates (represented for example by axis  511 ) and five horizontally-separated or “x” coordinates (represented for example by axis  513 ). Note that typically a grid is much larger, and a five-by-five array of grid intersections is depicted simply for purposes of illustration. Each intersection between a vertical axis and a horizontal axis defines a grid point, such as point  515 . Each point thus has a coordinate set associated with it, expressed as p(x,y,n) in  FIG.  5 A . The value “n” in this example refers to the η th  pass of a print head, i.e., grid points can optionally be repeated during a printing process or made respective to different print heads or print head passes. Given this coordinate system, points seen on the top line of the grid in this example have coordinates p(x,y,n), p(x+1,y,n), p(x+2,y,n), p(x+3,y,n) and p(x+4,y,n); each depicted point in this example is thus a possible droplet coordinate associated with one pass of a single print head. Naturally, this coordinate system is exemplary only, and any type of coordinate system can be used. In  FIG.  5 A , a solid dot at a particular grid point (such as at point  515 ) indicates that, according to a selected or calculated halftone pattern, an ink jet droplet is to be dispensed at that point, while a hollow circle at a grid point (such as at point  517 ) indicates that no ink droplet is to be dispensed at that point. For the halftone pattern represented by  FIG.  5 A , for example, ink will be dispensed at point  515  but not at point  517 . As mentioned, in one embodiment, each grid point, such as point  515 , corresponds to an individual print cell; in other embodiments, this need not be the case. The depicted grid coordinates and “dot” system should not be confused with ultimate extent of area coverage from ink on a printable surface of the substrate. That is, ink as a fluid will spread and cover a larger surface area than represented by the dots  515  and  517  seen in  FIG.  5 A , a result which is referred to as “dot gain.” The larger the dot gain, the greater the spreading of each ink droplet. In the example presented by  FIG.  5 A , assuming consistent grid spacing, the minimum dot gain should at least be sufficient to allow the minimum halftone droplet density (e.g., given ink viscosity, manufacturer grid specification and other particulars) to produce a continuous film. In practice, where a continuous film is desired, the dot gain will typically be much larger than the distance between closest grid points, e.g., sufficient to account for no ink printed at the substantial majority of the print cells, and with error diffusion relied upon (given ink viscosity) to provide homogeneity in the finished layer. For example, in a hypothetical case where every grid point exactly corresponds to a respective print cell, if every print cell were assigned the same grayscale value (e.g., “50%”), then half of the print cells would receive printed ink and half would not, with error diffusion (and ink droplet spreading) resulting in a homogeneous layer thickness. 
     By comparing the halftone pattern  509  of  FIG.  5 A  to a halftone pattern  519  seen in  FIG.  5 B , one can observe relative effects of FM halftoning. In the case of these FIGS, the ejected droplets are all depicted to be the same size, so for a thicker layer, a denser droplet pattern is used (e.g., more solid dots at grid intersections), and for a thinner layer, a less dense droplet pattern is used (e.g., fewer solid dots at grid intersections).  FIG.  5 A  shows an approximately 50% density of droplets that will achieve this effect, whereas  FIG.  5 B  shows that all grid coordinates (such as at point  515 ) have a solid circle, indicating a droplet firing at the particular grid coordinate. The depiction in  FIGS.  5 A and  5 B  might therefore correspond to respective grayscale values of 127 and 255, respectively (in a system having 256 possible values), or 50% and 100% (in a percentage based system). Again, other numbering schemes are also possible and it should be understood that the correspondence between layer thickness and droplet density may be dependent on dot gain and/or may be nonlinear; for example, where the minimum number of droplets for the depicted 25 gridpoints needed to obtain continuous coverage is “5,” the halftone pattern of  FIG.  5 A  might correspond to a grayscale value of 40% ((13-5)/20). 
     Note that the “grid” typically represents all possible firing positions of a group of ink jet nozzles and that each grid point in the halftone print image uses exactly 1-bit, denoting whether or not a droplet is to be ejected; thus, different “x” separations depending on embodiment will represent different nozzle firing times and/or firing from different print heads and/or different print head passes. A nozzle error (e.g., failure to fire) will appear as a regular pattern and can be detected through errors in a deposited layer. Reflecting back on the discussion earlier, related to error correction, if it is determined in practice that a particular nozzle does not operate, the depicted grid might be printed with errors that would be observed as thickness variation in the deposited layer. To mitigate this error, the halftone pattern(s) (or grayscale value(s)) could be adjusted so as to increase ejected ink volume for adjacent grid positions, or otherwise change drop shape, frequency or firing time. Mitigation is seen in  FIG.  5 E  for example, where it is noted that droplets  535  (from adjacent working nozzles) are deliberately larger to account for missing droplets  533  that should have been printed by a defective nozzle. Alternatively, per  FIG.  5 F , if a relatively sparse droplet pattern is applied (e.g., per the example of  FIG.  5 A ) but a nozzle is misfiring and thus incapable of ejecting droplets at position  537 , the droplets can be moved into adjacent lines ( 539 / 541 ) printed by working nozzles to maintain local droplet density. Other examples are also possible. Corrections can optionally be applied using any of the mentioned techniques, e.g., increasing or decreasing droplet size, moving droplets in a local area, adjusting electrical firing pattern for a nozzle, adding print head passes, increasing size or shape of selected droplets, and so forth. 
       FIG.  5 C  provides a third example halftone pattern example,  521 . Taken together with pattern  509  seen in  FIG.  5 A ,  FIG.  5 C  provides an example of amplitude modulated (“AM”) halftoning, where apparent droplet size is varied by providing a variable concentration (or cluster) of droplets, depending on grayscale value(s). For example, a concentration of dots centered at point  525  represents the same ink volume as the pattern from  FIG.  5 A , with individual droplets again fired on a binary decision basis, but with the relative concentration of droplets regionally varied. AM halftoning can therefore also optionally be used to vary layer thickness over an area of substrate. As with the examples before, thickness data for a desired layer can be converted to grayscale values, and the grayscale values can then be mapped to a halftone pattern; where AM halftoning is used, larger grayscale values result in a generally corresponding area of the substrate receiving larger apparent droplets. 
       FIG.  5 D  provides a grid depiction used to illustrate optional variation of halftone patterns to “stitch” together adjacent tiles of the substrate, to avoid Mura effect. In such an optional embodiment, halftone patterns for each of multiple “tiles” can be made dependent on patterns selected for adjacent tiles to provide for seamless droplet densities across tiles. For example,  FIG.  5 D  shows a hypothetical droplet deposition pattern  541  where a first region  543  is seen to correspond to the pattern of  FIG.  5 A  (approximately 50% halftoning) and where a second region  545  has a similar halftone pattern, also providing 50% density. Generally speaking, this FIG. represents a situation where different regions of the substrate receive independently generated halftone patterns, and where it is desired to “stitch” adjacent patterns together in a manner that is complementary, i.e., to avoid Mura. For region or “tile”  545 , the halftone pattern is therefore seen to be varied (e.g., inverted in this case) and selected such that seamless blending between tiles  543  and  545  occurs. To provide an example, if the pattern from  FIG.  5 A  was selected for both print regions or tiles (i.e.,  543  and  545 ), then each of adjacent grid coordinate pairs p(x+4,y,n) and p(x+5,y,n), p(x+4,y+3,n) and p(x+5,y+3,n) and p(x+4,y+5,n), p(x+5,y+5,n) would be represented using black-filled circles, corresponding to a local increase in droplet density. By selecting the halftone pattern for tile  545  in a manner dependent on the pattern selected for tile  543 , an appropriate pattern can be selected that provides for seamless transitions in droplet pattern between tiles. There are also other techniques for achieving variation, such as rotation of halftone patterns (e.g., using the techniques discussed above in connection with  FIGS.  3 A-C ), and so forth. Note that as depicted in  FIG.  5 D , both tiles use a common grid, such as represented by a common horizontal axis  511 ; this facilitates seamless stitching so as to avoid existence of a defect in between tiles. Tiles (i.e., independent halftone pattern selection for different, abutting substrate regions) can be used in one embodiment, but are, generally speaking, not required to implement the techniques described herein. 
     The various halftone patterns introduced above for  FIGS.  5 A- 5 F  are provided as illustrative examples of halftone patterning only. Many additional patterns can be conceived for a given grayscale value (or ink volume). Any particular halftone pattern (or multiple patterns for respective tiles) can be adjusted to correct for errors and otherwise promote uniformity in the fabricated layer. 
       FIG.  6 A  provides a table  601  that exemplifies a number of print cells, such as print cell  603 . Note that each cell contains a “grayscale” value, such as the value “203” depicted within print cell  603 . All print cells having a non-zero value represent the deposition area that is to receive the layer material to be jetted, i.e., each numerical value represents a layer thickness for a substrate region corresponding to the x-y position of the corresponding print cell, where thickness has been converted to a grayscale value. This value can be empirically mapped in advance to the desired thicknesses (e.g., 1.0 micron thickness to a 10% or “25.5” grayscale value as a hypothetical example), with such mapping possibly varying dependent on ink, printer, temperature, process and other parameters. Alternatively, as the end goal is that the assigned halftone pattern should provide an ink volume that will correspond to desired thickness, variable mapping can be provided between the assigned grayscale values and halftone pattern selection. Thus, in one embodiment, the grayscale values assigned to various thicknesses are fixed (e.g., 10% of maximum value per micron of thickness, following the hypothetical just presented) but with a variable mapping between each grayscale value and halftone pattern selection. Other variations are also possible. 
     Note that, as alluded to earlier, there exist alternate error correction techniques (i.e., besides adjustment of individual nozzle particulars). Thus,  FIG.  6 B  shows a grayscale image  611  that is similar to  FIG.  6 A , but where the last row (i.e., represented by print cell  603 ) has had its grayscale values increased, i.e., by “5” in this hypothetical example. Assuming a left to right scanning motion relative to the orientation of  FIG.  6 B , if it were determined (e.g., empirically or automatically) that nozzles corresponding to this last row tended to produce low volume drops, the grayscale data could be increased for the affected print cells such that, when printed, any aberrations in layer thickness are corrected. Conversely, if a particular row of print cells featured high drop volumes, it would be possible to artificially decrease grayscale values pertinent to affected print cells so as to planarize the resultant layer. Such a technique is especially useful where print cell size corresponds to each point of the halftone/print grid. Note that such adjustment need not be done by row or column or by scan path, i.e., it is possible to apply error adjustment on the basis of a map representing all or part of a printing substrate to adjust the grayscale values assigned to select print cells. As will be discussed below and elsewhere herein, such techniques can also be employed to vary edge build-up, i.e., to promote uniformity right up to a boundary or edge of the deposited layer. 
       FIG.  7 A  provides a graph, generally designated by numeral  701 , showing thickness profiles of fabricated films obtained with a stylus profilometer, useful in connection with the calibration process seen in  FIG.  4 C . Following the production of actual test layers of material, or simulation of those layers, grayscale values corresponding to an ink volume can be correlated with different steps in layer thickness. For example, a first curve  703 , representing a 1.0 micron thick layer, is associated with a grayscale value representing an 8% fill (or 8% of maximum print cell ink volume for a given pass or operation). Note that the film is continuous, i.e., there are no gaps in the center of the layer represented by curve  703 , which is seen to have substantially uniform thickness. For a subsequent fabrication process, if a layer thickness of 1.0 micron was assigned by received layout data for the deposited layer, this quantity of 1.0 micron would be converted to a a grayscale value for each print cell, as appropriate, and the grayscale value for print cells in a locality would then be applied to select a halftone pattern that would distribute droplets to various halftone grid points associated with that locality in order to achieve a uniform deposited layer (following droplet spreading). Similarly, a second curve  705  is seen to represent a uniform 2.0 micron thick layer, corresponding to 16% fill. Based on such test or calibration data for the particular process, a halftone pattern correlated to 16% ink volume for a particular substrate region might be generated to produce a 2.0 micron thick layer. Mappings between layer thickness values and/or grayscale values and/or halftone pattern selection can also be extrapolated using this process; as an example, if layout data called for a 1.5 micron thick encapsulation layer, grayscale values selected to correspond to a point roughly between these two values (12%) could be applied (e.g., halfway between 8% and 16%). Other illustrated curves  707 ,  709 ,  711  and  713 , respectively corresponding to 3.0, 4.0, 5.0 and 6.0 micron-thick layers are associated with grayscale values of 24%, 32%, 40% and 50%, respectively. By specifically matching different grayscale values to respective layer thicknesses, and associating halftone patterning used to deliver a corresponding amount of ink to a print cell, a designer can customize ink deposition to any desired thickness in a manner that will lead to predictable results; this provides a high degree of control over thickness of material deposited via fluidic ink. 
     In many applications, it is also desirable to provide a crisp, straight edge at border regions. For example, if a halftone pattern representing a low droplet density is selected for a border region, then it is possible, given ink and deposition properties, that the deposited layer will have a jagged, tapered or interrupted edge. To mitigate this possibility, in one embodiment, software detects print cells that would produce such an edge and adjusts halftoning (i.e., as a function of grayscale value gradient) to provide a crisp, straight edge that, in effect, frames the deposited layer. For example,  FIG.  7 B  provides a box  725  representing a corner of a deposited layer, with grid points not shown. To produce a thin film, the halftone patterning can be made relatively sparse in area  727 . If used in border regions  729 ,  731 , and  733  this density may produce a jagged edge. Thus, the density of droplets in areas  729 ,  731  and  733  can be purposely increased to improve edge linearity. If box  725  represents a print cell along an intermediate, left edge of a deposited layer, it would suffice to increase the density in area  729 . 
     Note that in addition to adjusting gray scale values for border regions, it is also possible to adjust halftoning applied to such a region. For example,  FIG.  7 C  shows an exemplary halftone pattern  741  that could be used where (as in the case of box  733  of  FIG.  7 B ), the region represents the corner of a deposited film; note that  FIG.  7 C  is similar to  FIGS.  5 A- 5 F  in its use of a grid and solid fill circle to denote a droplet ejection point. The particular halftone pattern represented in  FIG.  7 C  represents the same ink volume as the pattern seen in  FIG.  5 A  (i.e., 13 of 25 possible droplets ejected). However, the pattern in  FIG.  7 C  features relatively dense use of droplets along a top edge  743  of the substrate and a left edge  745  of the film, while interior region  747  is left relatively sparse, i.e., to produce relatively crisp left and upper edges. 
     Note that the use of such framing or “fencing” techniques is not required for all embodiments, and it is within the capabilities of one of ordinary skill in the art to determine the best strategy for a particular application, ink and process technology. 
       FIG.  7 D  represents a graph  751  that illustrates how grayscale image adjustment can be used to shape layer edges. More specifically, three curves  753 ,  755  and  757  are presented in  FIG.  7 D , obtained using stylus profilometer measurements of fabricated 6.0 micron encapsulation layers. The differences between these curves were produced by varying the grayscale values applied to print cells that abut edges. Relative to a baseline represented by curve  753 , curve  755  represents a process where the grayscale value (and associated ink volume for the print cell) is decreased on approach to a boundary in the encapsulation layer (e.g., before the encapsulation layer periphery). By contrast, curve  757  represents a process where the grayscale value is increased for print cells abutting the same boundary; note that layer thickness actually increases slightly immediately before the boundary, e.g., at x positions of 2000 µ and 17000 µ. By adjusting the grayscale values for border regions, a designer can adjust edge buildup at layer boundaries in a desired manner, including for purposes of providing a uniform layer thickness or surface, or smoothing or enhancing transitions. Note that the amount of the ink buildup adjacent to the layer edges will be largely dependent on ink properties, such as surface tension (and its dependence on temperature). For example, some inks may naturally form a lip, or so-called capillary ridge, (e.g., such as represented at point  759  of curve  757 ); in such an event, the grayscale adjustment process just described can be applied so as to remove this lip, e.g., to help tailor thickness of the ultimate layer by decreasing grayscale values for print cells abutting a layer edge, such that the profile of the permanent layer more closely matches curve  753 . 
     Returning briefly to the discussion of edge enhancement (see the discussion of  FIG.  7 C , above), it is also possible to employ multiple processes to tailor a layer’s edge profile.  FIG.  7 E  shows a portion of a substrate  761  that is to have a central region  763  of uniform layer thickness, a border region  765  of “adjusted” droplet density (i.e., selected so as to avoid edge buildup) and a set of fencing clusters  767  selected to provide edge uniformity. Perhaps otherwise stated, central region  763  represents an area of substantially uniform ink volume density, border region  765  represents an area of adjusted ink density (e.g., reduced density) relative to the central region, and fencing clusters  767  represent a relatively dense ink density selected to provide sharp, well-defined layer edges. In the presented example, halftoning might be performed based on uniform grayscale values in the central region (e.g., subject perhaps to nozzle error correction or underlying substrate geography correction, depending on embodiment) and adjusted grayscale values in the border region (e.g., selected so as to avoid edge buildup “horns”  715 , seen in  FIG.  7 A ). Halftoning can be based on the entire collection, or for example, the central and border region only (i.e., with fencing enforced following, and irrespective of, halftoning process). As should be appreciated by this example, many variations are possible which rely on grayscale and/or halftone variation in order to tailor edge buildup and/or provide for desired edge characteristics. 
     Naturally, while this example has been discussed in terms of an encapsulation layer, these same principles can be applied to the formation of any desired layer. For example, it is expressly contemplated that the described printing principles can be used to fabricate any of the HIL, HTL, EML, ETL or other layers of an OLED device, for example, by way of illustration, with respective print wells or on another patterned or unpatterned basis. Some examples will be discussed further below. 
       FIGS.  8 A- 8 E  are used to narrate an exemplary fabrication process. As implied by  FIG.  8 A , it should be assumed for this narration that it is desired to fabricate an array of flat panel devices. A common substrate is represented by numeral  801 , and a set of dashed-line boxes, such as box  803 , represents geometry for each flat panel device. A fiducial, preferably with two-dimensional characteristics, is formed on the substrate and used to locate and align the various fabrication processes. Following eventual completion of these processes, each panel ( 803 ) will be separated from the common substrate using a cutting or similar process. Where the arrays of panels represent respective OLED displays, the common substrate  801  will typically be glass, with structures deposited atop the glass, followed by one or more encapsulation layers. Light emission may occur through the glass or the encapsulation layers (depending on design). For some applications, other substrate materials can be used, for example, a flexible material, transparent or opaque. As noted, many other types of devices can be manufactured according to the described techniques. 
       FIG.  8 B  is used to help illustrate fabrication of OLED panels. Specifically,  FIG.  8 B  shows the substrate in a later stage of the fabrication process, after structures have been added to the substrate. The assembly is generally represented by numeral  811 , and is seen to still feature an array of panels on a common substrate. Features specific to one panel will be designated using a numeral followed by a respective letter, for example, the letter “A” for a first panel, “B” for a second panel, and so forth. Each panel has a respective portion of the substrate,  812 A/ 812 B, for example, and an active region  813 A/ 813 B  that contains light emitting layers. Generally speaking, the respective active region will include electrodes and luminescent layers necessary to provide pixilation and associated routing of electrical signals, such as for control and power. This routing conveys power and control information between respective terminals (e.g.,  815 A/B,  816 A/B) associated with a terminal block  817 A/ 817 B and the active region for the respective panel. Typically, the encapsulation layer must provide a protective “blanket” over the active region only (i.e., to seal electroluminescent materials) while permitting unimpeded external access to the terminal block  817 A/B. Thus, a printing process must deposit liquid ink in a manner that reliably and uniformly covers the active region ( 813 A/ 813 B) without gaps, holes or other defects, while at the same time reliably and uniformly not covering the terminal block  817 A/ 817 B. The active region is thus said to form a “target region” that will receive deposited ink to form the desired layer, while the terminal block forms part of an “exposed region” that will not receive the ink. Note in  FIG.  8 B  the use of numeral  818  to denote an xyz coordinate system and the use of numeral  819  to reference respective sets of ellipses to indicate presence of any number of panels replicated in x and y dimensions of the array. 
       FIG.  8 C  illustrates a cross-section of the assembly  811 , taken along lines C-C from  FIG.  8 B . In particular, this view shows the substrate  812 A of panel A, the active region  813 A of panel A, and conductive terminals ( 815 A) of panel A used to effect electronic connection to the active region. A small elliptical region  821  of the view is seen magnified at the right side of the FIG. to illustrate layers in the active region above the substrate  812 A. These layers respectively include an anode layer  829 , a hole injection layer (“HIL”)  831 , a hole transport layer (“HTL”)  833 , an emissive or light emitting layer (“EML”)  835 , an electron transport layer (“ETL”)  837  and a cathode layer  838 . Additional layers, such as polarizers, barrier layers, primers and other materials can also be included. When the depicted stack is eventually operated following manufacture, current flow removes electrons from the EML, and resupplies of those electrons from the cathode to cause the emission of light. The anode layer  829  typically comprises one or more transparent electrodes common to several color components and/or pixels to attract and remove electrons; for example, the anode can be formed from indium tin oxide (ITO). The HIL  831  is typically a transparent, high work function material that will form a barrier to unintended leakage current. The HTL  833  is another transparent layer that passes electrons from the EML to the anode, while leaving electrical “holes” in the EML. Light generated by the OLED originates from recombination of electrons and holes in the EML material  835 ; typically, the EML consists of separately-controlled, active materials for each of three primary colors, red, green and blue, for each pixel of the display. In turn, the ETL  837  supplies electrons to the EML from the cathode layer to each active element (e.g., each red, green or blue color component). Finally, the cathode layer  838  typically consists of patterned electrodes to provide selective control to color component for each pixel. Lying at the rear of the display, this layer is typically not transparent, and can be made from any suitable electrode material. 
     As noted, layers in the active region can be degraded through exposure to oxygen and/or moisture. It is therefore desired to enhance OLED life by encapsulating these layers, both on faces or sides ( 822 ) of those layers opposite the substrate, as well as lateral edges, designated by numeral  823 . The purpose of encapsulation is to provide an oxygen and/or moisture resistant barrier, as mentioned. 
       FIG.  8 D  shows an aggregate structure  839  where encapsulation  840  has been added to the substrate. Note that the encapsulation  840  now encloses faces  822  and lateral edges  823  relative to the substrate  812 A and that the encapsulation extends laterally to occupy a deposition area larger than the underlying active layers; at a terminus of this area, the encapsulation forms a gradient or border region to help enclose/seal lateral edges of the active region  813 A. This is observed in detail at the left side of  FIG.  8 D  within a magnified elliptical region  841 . As seen in this expanded view, the encapsulation comprises a number of thin layers, for example, alternating organic and inorganic layers, which provide a barrier against moisture and oxygen. The organic encapsulation layers can be advantageously deposited using the techniques introduced above, with the thickness of each individual layer regulated using the mentioned techniques. Relative to a particular organic encapsulation layer  842 , a first region  843  overlies underlying structures, such as the mentioned electrodes and the other OLED layers discussed above. A second region  845  operates as a buffer region, i.e., to maintain a substantially uniform surface  846  that is planar with the first region  843 . Optionally, deposited thickness can be the same in both of regions  843  and  845 , but this need not be the case for all deposition processes. Irrespective of region, an ink jet printing process, using halftoning to translate layer thickness, can be used to control thickness and promote uniformity of the particular encapsulation layer  842 . Finally, a third, gradient or border region  847  represents a transition to an exposed area of the underlying substrate (e.g., to provide electrical terminals for the active region). Numeral  849  indicates an associated taper in the encapsulation surface as it transitions to exposed substrate. 
       FIG.  8 E  is used to help illustrate the use of processing to adjust material thickness at layer edges in the context of an OLED panel. These processes were generally introduced earlier in connection with  FIGS.  7 B- 7 E . For example, in an encapsulation process such as the one discussed, it can be desirable to ensure consistent layer thickness all the way to a planned encapsulation periphery in order to provide for reliable edge sealing of any underlying sensitive material layers. Note that the use of “fencing” as was seen in  FIG.  7 E  is not separately seen in this FIG., though the same fencing process could be used here. In  FIG.  8 E , the substrate is once again observed in a plan view, that is, from the same perspective as seen in  FIGS.  8 A and  8 B  (though depiction of the electrical terminals is omitted). Note the use of a fiducial  851  to align processes such that an organic encapsulation layer is correctly printed over underlying substrate. The target region (representing area where the encapsulation layer is to be deposited) is seen to comprise regions  843  and  845  from  FIG.  8 D . Rather than have undesired edge effects given spreading of deposited ink and the effect of surface energy/tension of that ink, the grayscale image can be adjusted (i.e., before printing) so as to change grayscale values for individual print cells along the layer’s edge and, in so doing, change the edge profile at a layer periphery. For example, grayscale values within region  845  can be increased as depicted in  FIG.  8 E  so as to optionally increase ink volume in areas approaching the boundary. Note in this regard that the target region can initially be associated with a particular thickness, for example, represented by hypothetical grayscale value “220” in this example. If it is determined empirically that due to ink spreading, a transition (for example, at the boundary between regions  845  and  847 ) provides insufficient coverage, the grayscale value in that area can be selectively increased to provide mitigation, for example, by increasing the grayscale value (e.g., from “220” to “232” in  FIG.  8 E ) for one or more rows or columns of print cells representing the layer periphery. As referenced earlier, corrections can be stored as a correction image (e.g., as the corrections might, depending on application, vary as a function of process, temperature, ink and other factors), or they can optionally be incorporated into the layout data, grayscale image or other stored data. Note that where multiple boundary conditions are present, for example, intersection of two borders, it may be desired to provide further adjustment, such as the depicted grayscale value of “240” for corner print cell  863 . Clearly many possibilities exist. By adjusting droplet density in these border regions, the techniques introduced above permit customized control over the layer edges in any manner suitable to the particular deposition process at issue, for example, to facilitate edge sealing of flat panel devices. Note that it is also possible for software to automatically provide for adjusted print cell fill (i.e., to adjust grayscale values) according to a selected scaling factor any time the software detects print cells within a defined distance from a layer edge. Fencing can be added before or after a grayscale image is sent for halftone generation, depending on desired embodiment or effect. 
       FIG.  9    presents a method generally represented by numeral  901 . In this example, it should be assumed that it is desired to deposit a layer as part of an encapsulation process of a device such as a flat panel display or a solar panel. The encapsulation is used to help protect internal materials of the device from exposure to moisture or oxygen, thus prolonging expected lifetime of the device. This application is but one application for disclosed techniques, and nearly any type of layer (organic or inorganic), for nearly any type of device that is to receive a printed layer of material can benefit from the teachings herein. 
     It will be assumed for this discussion that the layer will be an organic material deposited over a substrate, as part of a repeating stack of alternating organic and inorganic materials layers; as many pairs of such layers are built up, this stack will encapsulate sensitive materials against a specific layer of the substrate. For example, in an OLED device, an electrode, one or more emissive layers, a second electrode and alternating organic/inorganic encapsulation layer pairs can be deposited over a layer of glass, with the encapsulation (once finished) sealing the emissive layers (including lateral edges of the emissive layers) against the glass layer. Typically, it is desired to minimize exposure of the assembly to contaminants during the fabrication process until the encapsulation has been completed. To this effect, in a process described below, while the various layers are added, the substrate is kept in one or more controlled environments until the encapsulation has been completed. The encapsulation can be formed using a multi-chambered process where the substrate is subjected to alternating deposition processes to form the organic and inorganic layer pairs. In this example, it is assumed that the techniques introduced above are applied to deposit an organic layer within the encapsulation stack and that this layer is typically deposited in liquid form and then hardened or otherwise cured to form a permanent layer prior to addition of the next (inorganic) layer. An ink jet printing process can be advantageously used to deposit this organic layer according to the principles introduced above. 
     Note that a “controlled atmosphere” or “controlled environment” as used herein refers to something other than ambient air, i.e., at least one of the composition or the pressure of a deposition atmosphere is controlled so as to inhibit introduction of contaminates; an “uncontrolled environment” means normal air without means of excluding unwanted particulates. In connection with the process depicted by  FIG.  9   , both the atmosphere and pressure can be controlled, such that deposition occurs in the presence of an inert material, such as nitrogen gas, at a specified pressure, free from unwanted particulates. In one embodiment, a multi-tool deposition mechanism can be used to alternately deposit organic and inorganic layers of an encapsulation of sensitive materials, for example, using different processes. In another embodiment, a multi-chambered fabrication mechanism is used, such that some processing (e.g., active layer or inorganic encapsulation layer deposition) occurs in one chamber while a printing process using the principles introduced herein is applied in a different chamber; as will be discussed below, a mechanical handler can be used to automate transportation of the substrate from one chamber to the next without exposing the substrate to an uncontrolled environment. In still another embodiment, continuity of the controlled environment is interrupted, i.e., the other layers are fabricated elsewhere and the substrate is loaded into a deposition chamber, a controlled atmosphere is introduced, the substrate is cleaned or purified, and then the desired layer is added. Other alternatives are also possible. These different embodiments are variously represented by  FIG.  9   .  FIG.  9    expressly shows two optional process integrations, including integration ( 903 ) of fabrication of an inorganic encapsulation layer (and/or one or more other layers, such as active layers) with deposition of an organic encapsulation layer in a secured environment (e.g., not exposed to uncontrolled atmosphere) and/or integration ( 904 ) of the deposition of the organic encapsulation layer with a subsequent drying, curing or other process, to solidify the organic encapsulation layer and otherwise finish the layer as a permanent structure. For each optional integration process, the mentioned steps can be performed in one or more controlled environments that are uninterrupted by exposure to an uncontrolled environment (e.g., ambient air). For example, a multichamber fabrication device with means for controlling the deposition environment can be used, as mentioned. 
     Irrespective of embodiment, the substrate is positioned for patterning and/or printing as appropriate. Accordingly, registration is first performed ( 905 ) using fiducials (or recognizable patterns) on the substrate. Typically, a fiducial will consist of one or more alignment marks that identify each region that is to be printed. As an example, as introduced earlier (see, e.g., element  805  from  FIG.  8 A ), several flat panels can be fabricated together and cut from one die or common substrate; in such a case, there might be a separate fiducial for each panel, positioned so that the printing mechanism and associated process can be precisely aligned with any pre-patterned structures for each panel. Note, however, that fiducials can be used even where a single panel is to be fabricated. As will be further discussed below, the deposition system can include an imaging system having a known positional relationship relative to the printing mechanism, with digital images of the substrate fed to a processor or CPU and analyzed using image analysis software to precisely identify the fiducials. In one optional variation, there are no special marks added to the substrate, i.e., the printing system recognizes its target by simply identifying any existing structures (such as any previously-deposited particular electrode or particular electrodes) and aligns to this pattern. Note also that, advantageously, each fiducial represents a two dimensional pattern, permitting correction of position and any substrate skew prior to deposition. 
     One or more layers are then added to the substrate, for example, consisting of one or more emissive layers, electrode layers, charge transport layers, inorganic encapsulation layers, barrier layers and/or other layers or materials ( 906 ). As mentioned, deposition in one embodiment is performed in a controlled environment ( 907 ), optionally in an inert atmosphere ( 909 ) such as nitrogen gas or a noble gas. Following this processing, an organic encapsulation layer is deposited as a liquid ink, as represented by numeral  911 . In contradistinction to other possible processes (e.g., used to add a mask layer), the ink in this embodiment directly provides the material that will form the desired layer following cure, hardening, etc. Note also that the printing process is also advantageously performed in a controlled environment ( 907 ), such as in an inert atmosphere ( 909 ), and that the processes can be repeated and alternated as denoted by the fact that connection arrows are bidirectional; for example, a stack of inorganic and organic encapsulation layer pairs can be built up as introduced earlier. 
       FIG.  9    also shows various process options to the right of process box  911 . These options include the use of a multi-atmosphere process ( 913 ), the deposition of the organic encapsulation layer as a liquid ink ( 915 ), the deposition of the organic encapsulation layer atop a non-planar substrate ( 917 ), the use of a target deposition region of the substrate (that will receive the encapsulation layer) and an exposed region of the substrate (that will not be enclosed by the encapsulation layer) ( 919 ) and the generation of a border region (or gradient region) that will seal lateral edges of any underlying layers (e.g., from halftoning specific to a border region or gradient filtering,  921 ), as discussed above in connection with  FIGS.  7 A- 7 E . 
     Once each organic encapsulation layer has been deposited, as discussed above, the layer is dried or otherwise cured ( 925 ) to render the layer permanent. In one embodiment, the organic encapsulation layer is deposited as a liquid monomer or polymer, and following deposition, an ultraviolet light is applied to the deposited ink to cure the material and harden it and form a layer of the desired thickness. In another possible process, the substrate is heated to evaporate any solvent or carrier for suspended materials, which then forms a permanent layer having the desired thickness. Other finishing processes are also possible. 
     Finally, once all encapsulation processes (including the desired number of organic and inorganic layer pairs) have been completed, the entire substrate can be removed from the controlled environment, per numeral  927 . 
     While the described process can be used to deposit encapsulation for sensitive materials, as discussed above, the same process can also be used to deposit many different and other types of layers as well, including inorganic layers and layers for non-electronic devices. 
     As shown by the description above, halftoning processes can advantageously be used to fabricate layers of controlled thickness using print cell-to-print cell and/or nozzle-to-nozzle control over ink densities. More specifically, the described techniques are especially useful where a liquid ink is used to deposit layer material of a desired thickness. By selecting grayscale values and generating halftone patterns that provide complete coverage (that is, to deposit a layer of sufficient density to avoid defects or holes), a layer can be inexpensively and efficiently applied with localized control over thickness and uniformity, e.g., notwithstanding a liquid deposition medium and any subsequent cure process. The disclosed techniques are particularly useful for the deposition of homogenous layers such as blanket coatings, encapsulation layers, and other layers where feature size is relatively large (e.g., tens of microns or more) compared to the widths and feature definitions of any underlying electronic pathways. As also noted above, the disclosed techniques can be embodied in different forms, for example, as software (instructions stored on non-transitory machine-readable media), as a computer, printer or fabrication mechanism, as an information file (stored on non-transitory machine-readable media) useful in instructing fabrication of such a layer, or in a product (e.g., a flat panel) made dependent on use of the described techniques. Optionally also, error correction techniques can be used to correct for droplet aberration from individual nozzles, to blend adjacent halftone patterns (e.g., for adjacent tiles), to correct grayscale values to planarize the deposited layer, or for other effect. Several embodiments rely on error diffusion to ensure layer homogeneity and distribute droplet patterns in a manner that averages grayscale values for neighboring print cells. Again, many other applications will occur to those skilled in the art. 
     The foregoing description and in the accompanying drawings, specific terminology and drawing symbols have been set forth to provide a thorough understanding of the disclosed embodiments. In some instances, the terminology and symbols may imply specific details that are not required to practice those embodiments. The terms “exemplary” and “embodiment” are used to express an example, not a preference or requirement. Note that some elements described above can be described as “means for” performing a particular function. Generally, such “means” includes structure described above, including, where and as applicable, instructions stored on non-transitory machine-readable media (e.g., software or executable instructions) that are written in a manner that will, when executed, cause at least one processor to perform a particular function. Without limitation, specified functions can also be performed by dedicated equipment, such as special purpose analog or digital machines. 
     As indicated, various modifications and changes may be made to the embodiments presented herein without departing from the broader spirit and scope of the disclosure. For example, features or aspects of any of the embodiments may be applied, at least where practical, in combination with any other of the embodiments or in place of counterpart features or aspects thereof. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.