Method of creating MEMS device cavities by a non-etching process

MEMS devices (such as interferometric modulators) may be fabricated using a sacrificial layer that contains a heat vaporizable polymer to form a gap between a moveable layer and a substrate. One embodiment provides a method of making a MEMS device that includes depositing a polymer layer over a substrate, forming an electrically conductive layer over the polymer layer, and vaporizing at least a portion of the polymer layer to form a cavity between the substrate and the electrically conductive layer. Another embodiment provides a method for making an interferometric modulator that includes providing a substrate, depositing a first electrically conductive material over at least a portion of the substrate, depositing a sacrificial material over at least a portion of the first electrically conductive material, depositing an insulator over the substrate and adjacent to the sacrificial material to form a support structure, and depositing a second electrically conductive material over at least a portion of the sacrificial material, the sacrificial material being removable by heat-vaporization to thereby form a cavity between the first electrically conductive layer and the second electrically conductive layer.

BACKGROUND

1. Field of the Invention

This invention relates to microelectromechanical systems for use as interferometric modulators. More particularly, this invention relates to systems and methods for improving the manufacture of interferometric modulators.

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by a gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed.

SUMMARY

The system, method, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Embodiments” one will understand how the features of this invention provide advantages over other display devices.

An embodiment provides a method of making a MEMS device that includes depositing a polymer layer over a substrate, forming an electrically conductive layer over the polymer layer, and vaporizing at least a portion of the polymer layer to form a cavity between the substrate and the electrically conductive layer.

Another embodiment provides an unreleased MEMS device that includes a substrate, a heat-vaporizable polymer over the substrate, and an electrically conductive layer over the heat-vaporizable polymer.

Another embodiment provides a method for making an interferometric modulator that includes providing a substrate, depositing a first electrically conductive material over at least a portion of the substrate, depositing a sacrificial material over at least a portion of the first electrically conductive material, depositing an insulator over the substrate and adjacent to the sacrificial material to form a support structure, and depositing a second electrically conductive material over at least a portion of the sacrificial material, the sacrificial material being removable by heat-vaporization to thereby form a cavity between the first electrically conductive layer and the second electrically conductive layer. Another embodiment provides an unreleased interferometric modulator made by such a method.

Another embodiment provides an unreleased interferometric modulator that includes a first means for reflecting light, a second means for reflecting light, a first means for supporting the second reflecting means, and a second means for supporting the second reflecting means, where the first supporting means comprises a sacrificial material, the sacrificial material being removable by heat-vaporization to thereby form a cavity defined by the first reflecting means, the second reflecting means, and the second supporting means.

Another embodiment provides an interferometric modulator that includes a substrate, a first electrically conductive material over at least a portion of the substrate, a second electrically conductive layer separated from the first electrically conductive layer by a cavity, and a nonconductive support structure arranged over the substrate and configured to support the second electrically conductive layer. In this embodiment, at least one of the first electrically conductive layer, the second electrically conductive layer and the non-conductive support structure comprises a material that is etchable by xenon diflouride. Another embodiment provides an array of interferometric modulators that includes such an interferometric modulator. Another embodiment provides a display device that includes such an array of interferometric modulators. The display device of this embodiment further includes a processor configured to communicate with the array, the processor being configured to process image data, and a memory device configured to communicate with the processor.

These and other embodiments are described in greater detail below.

FIGS. 1 to 13are not to scale.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices.

A preferred embodiment provides methods of making interferometric modulators by using a sacrificial layer that contains a heat vaporizable polymer to form a gap between a moveable layer and a substrate.

One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated inFIG. 1. In these devices, the pixels are in either a bright or dark state. In the bright (“on” or “open”) state, the display element reflects a large portion of incident visible light to a user. When in the dark (“off” or “closed”) state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the “on” and “off” states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white.

The depicted portion of the pixel array inFIG. 1includes two adjacent interferometric modulators12aand12b. In the interferometric modulator12aon the left, a movable reflective layer14ais illustrated in a relaxed position at a predetermined distance from an optical stack16a, which includes a partially reflective layer. In the interferometric modulator12bon the right, the movable reflective layer14bis illustrated in an actuated position adjacent to the optical stack16b.

The optical stacks16aand16b(collectively referred to as optical stack16), as referenced herein, typically comprise of several fused layers, which can include an electrode layer, such as indium tin oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. The optical stack16is thus electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the above layers onto a transparent substrate20. In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable reflective layers14a,14bmay be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of16a,16b) deposited on top of posts18and an intervening sacrificial material deposited between the posts18. When the sacrificial material is etched away, the movable reflective layers14a,14bare separated from the optical stacks16a,16bby a defined gap19. A highly conductive and reflective material such as aluminum may be used for the reflective layers14, and these strips may form column electrodes in a display device.

With no applied voltage, the cavity19remains between the movable reflective layer14aand optical stack16a, with the movable reflective layer14ain a mechanically relaxed state, as illustrated by the pixel12ainFIG. 1. However, when a potential difference is applied to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable reflective layer14is deformed and is forced against the optical stack16. A dielectric layer (not illustrated in this Figure) within the optical stack16may prevent shorting and control the separation distance between layers14and16, as illustrated by pixel12bon the right inFIG. 1. The behavior is the same regardless of the polarity of the applied potential difference. In this way, row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies.

FIGS. 2 through 5illustrate one exemplary process and system for using an array of interferometric modulators in a display application.

FIG. 2is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor21which may be any general purpose single- or multi-chip microprocessor such as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessor such as a digital signal processor, microcontroller, or a programmable gate array. As is conventional in the art, the processor21may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application.

In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row1electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row2electrode, actuating the appropriate pixels in row2in accordance with the asserted column electrodes. The row1pixels are unaffected by the row2pulse, and remain in the state they were set to during the row1pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention.

FIGS. 4 and 5illustrate one possible actuation protocol for creating a display frame on the 3×3 array ofFIG. 2.FIG. 4illustrates a possible set of column and row voltage levels that may be used for pixels exhibiting the hysteresis curves ofFIG. 3. In theFIG. 4embodiment, actuating a pixel involves setting the appropriate column to −Vbias, and the appropriate row to +ΔV, which may correspond to −5 volts and +5 volts respectively. Relaxing the pixel is accomplished by setting the appropriate column to +Vbias, and the appropriate row to the same +ΔV, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at +Vbias, or −Vbias. As is also illustrated inFIG. 4, it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to +Vbias, and the appropriate row to −ΔV. In this embodiment, releasing the pixel is accomplished by setting the appropriate column to −Vbias, and the appropriate row to the same −ΔV, producing a zero volt potential difference across the pixel.

In theFIG. 5Aframe, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) are actuated. To accomplish this, during a “line time” for row1, columns1and2are set to −5 volts, and column3is set to +5 volts. This does not change the state of any pixels, because all the pixels remain in the 3-7 volt stability window. Row1is then strobed with a pulse that goes from 0, up to 5 volts, and back to zero. This actuates the (1,1) and (1,2) pixels and relaxes the (1,3) pixel. No other pixels in the array are affected. To set row2as desired, column2is set to −5 volts, and columns1and3are set to +5 volts. The same strobe applied to row2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again, no other pixels of the array are affected. Row3is similarly set by setting columns2and3to −5 volts, and column1to +5 volts. The row3strobe sets the row3pixels as shown inFIG. 5A. After writing the frame, the row potentials are zero, and the column potentials can remain at either +5 or −5 volts, and the display is then stable in the arrangement ofFIG. 5A. It will be appreciated that the same procedure can be employed for arrays of dozens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the systems and methods described herein.

FIGS. 6A and 6Bare system block diagrams illustrating an embodiment of a display device40. The display device40can be, for example, a cellular or mobile telephone. However, the same components of display device40or slight variations thereof are also illustrative of various types of display devices such as televisions and portable media players.

The display device40includes a housing41, a display30, an antenna43, a speaker45, a microphone46and an input device48. The housing41is generally formed from any of a variety of manufacturing processes as are well known to those of skill in the art, including injection molding, and vacuum forming. In addition, the housing41may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing41includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols.

The display30of the exemplary display device40may be any of a variety of displays, including a bi-stable display, as described herein. In other embodiments, the display30includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display30includes an interferometric modulator display, as described herein.

The components of one embodiment of the exemplary display device40are schematically illustrated inFIG. 6B. The illustrated exemplary display device40includes a housing41and can include additional components at least partially enclosed therein. For example, in one embodiment, the exemplary display device40includes a network interface27that includes an antenna43which is coupled to a transceiver47. The transceiver47is connected to the processor21, which is connected to conditioning hardware52. The conditioning hardware52may be configured to condition a signal (e.g. filter a signal). The conditioning hardware52is connected to a speaker45and a microphone46. The processor21is also connected to an input device48and a driver controller29. The driver controller29is coupled to a frame buffer28and to the array driver22, which in turn is coupled to a display array30. A power supply50provides power to all components as required by the particular exemplary display device40design.

The network interface27includes the antenna43and the transceiver47so that the exemplary display device40can communicate with one ore more devices over a network. In one embodiment the network interface27may also have some processing capabilities to relieve requirements of the processor21. The antenna43is any antenna known to those of skill in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 standard, including IEEE 802.11(a), (b), or (g). In another embodiment, the receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS or other known signals that are used to communicate within a wireless cell phone network. The transceiver47pre-processes the signals received from the antenna43so that they may be received by and further manipulated by the processor21. The transceiver47also processes signals received from the processor21so that they may be transmitted from the exemplary display device40via the antenna43.

In an alternative embodiment, the transceiver47can be replaced by a receiver. In yet another alternative embodiment, the network interface27can be replaced by an image source, which can store or generate image data to be sent to the processor21. For example, the image source can be a memory storage device such as a digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data.

The processor21generally controls the overall operation of the exemplary display device40. The processor21receives data, such as compressed image data from the network interface27or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor21then sends the processed data to the driver controller29or to the frame buffer28for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level.

In one embodiment, the processor21includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device40. The conditioning hardware52generally includes amplifiers and filters for transmitting signals to the speaker45, and for receiving signals from the microphone46. The conditioning hardware52may be discrete components within the exemplary display device40, or may be incorporated within the processor21or other components.

The driver controller29takes the raw image data generated by the processor21either directly from the processor21or from the frame buffer28and reformats the raw image data appropriately for high speed transmission to the array driver22. Specifically, the driver controller29reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array30. Then the driver controller29sends the formatted information to the array driver22. Although a driver controller29, such as a LCD controller, is often associated with the system processor21as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor21as hardware, embedded in the processor21as software, or fully integrated in hardware with the array driver22.

Typically, the array driver22receives the formatted information from the driver controller29and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display's x-y matrix of pixels.

In one embodiment, the driver controller29, array driver22, and display array30are appropriate for any of the types of displays described herein. For example, in one embodiment, the driver controller29is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, the array driver22is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, the driver controller29is integrated with the array driver22. Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, the display array30is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators).

The input device48allows a user to control the operation of the exemplary display device40. In one embodiment, the input device48includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone46is an input device for the exemplary display device40. When the microphone46is used to input data to the device, voice commands may be provided by a user for controlling operations of the exemplary display device40.

The power supply50can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, the power supply50is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, the power supply50is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, the power supply50is configured to receive power from a wall outlet.

In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver22. Those of skill in the art will recognize that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example,FIGS. 7A-7Eillustrate five different embodiments of the movable reflective layer14and its supporting structures.FIG. 7Ais a cross section of the embodiment ofFIG. 1, where a strip of metal material14is deposited on orthogonally extending support structures18. InFIG. 7B, the movable reflective layer14is attached to supports at the corners only, on tethers32. InFIG. 7C, the movable reflective layer14is suspended from a deformable layer34, which may comprise a flexible metal. The deformable layer34connects, directly or indirectly, to the substrate20around the perimeter of the deformable layer34. These connections may be referred to herein as support posts. The embodiment illustrated inFIG. 7Dhas support structures18that include support post plugs42upon which the deformable layer34rests. The movable reflective layer14remains suspended over the cavity, as inFIGS. 7A-7C, but the deformable layer34does not form the support posts18by filling holes between the deformable layer34and the optical stack16. Rather, the support posts18comprise a planarization material, which is used to form support post plugs42. The embodiment illustrated inFIG. 7Eis based on the embodiment shown inFIG. 7D, but may also be adapted to work with any of the embodiments illustrated inFIGS. 7A-7Cas well as additional embodiments not shown. In the embodiment shown inFIG. 7E, an extra layer of metal or other conductive material has been used to form a bus structure44. This allows signal routing along the back of the interferometric modulators, eliminating a number of electrodes that may otherwise have had to be formed on the substrate20.

In embodiments such as those shown inFIG. 7, the interferometric modulators function as direct-view devices, in which images are viewed from the front side of the transparent substrate20, the side opposite to that upon which the modulator is arranged. In these embodiments, the reflective layer14optically shields some portions of the interferometric modulator on the side of the reflective layer opposite the substrate20, including the deformable layer34and the bus structure44(FIG. 7E). This allows the shielded areas to be configured and operated upon without negatively affecting the image quality. This separable modulator architecture allows the structural design and materials used for the electromechanical aspects and the optical aspects of the modulator to be selected and to function independently of each other. Moreover, the embodiments shown inFIGS. 7C-7Ehave additional benefits deriving from the decoupling of the optical properties of the reflective layer14from its mechanical properties, which are carried out by the deformable layer34. This allows the structural design and materials used for the reflective layer14to be optimized with respect-to the optical properties, and the structural design and materials used for the deformable layer34to be optimized with respect to desired mechanical properties.

FIG. 8illustrates certain steps in an embodiment of a manufacturing process800for an interferometric modulator. Such steps may be present in a process for manufacturing, e.g., interferometric modulators of the general type illustrated inFIGS. 1 and 7, along with other steps not shown inFIG. 8. With reference toFIGS. 1,7and8, the process800begins at step805with the formation of the optical stack16over the substrate20. The substrate20may be a transparent substrate such as glass or plastic and may have been subjected to prior preparation step(s), e.g., cleaning, to facilitate efficient formation of the optical stack16. As discussed above, the optical stack16is electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the layers onto the transparent substrate20. In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device. In some embodiments, the optical stack16includes an insulating or dielectric layer that is deposited over one or more metal layers (e.g., reflective and/or conductive layers).

The process800illustrated inFIG. 8continues at step810with the formation of a sacrificial layer over the optical stack16. The sacrificial layer is later removed (e.g., at step825) to form the cavity19as discussed below and thus the sacrificial layer is not shown in the resulting interferometric modulator12illustrated inFIGS. 1 and 7. The formation of the sacrificial layer over the optical stack16may include deposition of a XeF2-etchable material such as molybdenum or amorphous silicon, in a thickness selected to provide, after subsequent removal, a cavity19having the desired size. Deposition of the sacrificial material may be carried out using deposition techniques such as physical vapor deposition (PVD, e.g., sputtering), plasma-enhanced chemical vapor deposition (PECVD), thermal chemical vapor deposition (thermal CVD), or spin-coating.

The process800illustrated inFIG. 8continues at step815with the formation of a support structure e.g., a post18as illustrated inFIGS. 1 and 7. The formation of the post18may include the steps of patterning the sacrificial layer to form a support structure aperture, then depositing a material (e.g., a polymer) into the aperture to form the post18, using a deposition method such as PECVD, thermal CVD, or spin-coating. In some embodiments, the support structure aperture formed in the sacrificial layer extends through both the sacrificial layer and the optical stack16to the underlying substrate20, so that the lower end of the post18contacts the substrate20as illustrated inFIG. 7A. In other embodiments, the aperture formed in the sacrificial layer extends through the sacrificial layer, but not through the optical stack16. For example,FIG. 7Cillustrates the lower end of the support post plugs42in contact with the optical stack16.

The process800illustrated inFIG. 8continues at step820with the formation of a movable reflective layer such as the movable reflective layer14illustrated inFIGS. 1 and 7. The movable reflective layer14may be formed by employing one or more deposition steps, e.g., reflective layer (e.g., aluminum, aluminum alloy) deposition, along with one or more patterning, masking, and/or etching steps. As discussed above, the movable reflective layer14is typically electrically conductive, and may be referred to herein as an electrically conductive layer. Since the sacrificial layer is still present in the partially fabricated interferometric modulator formed at step820of the process800, the movable reflective layer14is typically not movable at this stage. A partially fabricated interferometric modulator that contains a sacrificial layer may be referred to herein as an “unreleased” interferometric modulator.

The process800illustrated inFIG. 8continues at step825with the formation of a cavity, e.g., a cavity19as illustrated inFIGS. 1 and 7. The cavity19may be formed by exposing the sacrificial material (deposited at step810) to an etchant. For example, an etchable sacrificial material such as molybdenum or amorphous silicon may be removed by dry chemical etching, e.g., by exposing the sacrificial layer to a gaseous or vaporous etchant, such as vapors derived from solid xenon difluoride (XeF2) for a period of time that is effective to remove the desired amount of material, typically selectively relative to the structures surrounding the cavity19. Other etching methods, e.g. wet etching and/or plasma etching, may also be used. Since the sacrificial layer is removed during step825of the process800, the movable reflective layer14is typically movable after this stage. After removal of the sacrificial material, the resulting fully or partially fabricated interferometric modulator may be referred to herein as a “released” interferometric modulator.

While etching methods have been used to successfully remove sacrificial materials such as molybdenum or amorphous silicon to form cavities in MEMS devices such as interferometric modulators, there are drawbacks and disadvantages. One disadvantage of etching is that the size of the substrates that can be etched is usually small due to the environmental control requirements of the etching process including, for example, venting toxic and/or corrosive by-products, e.g., fluorine gas. Another disadvantage is that complete removal of some sacrificial materials may result in over etching and damage to neighboring structures. Such damage may be mitigated, e.g., by using an etch stop, but in some situations such additional structures may undesirably complicate the process. Another disadvantage is that use of materials that are etchable by XeF2may be limited in devices that are exposed to a XeF2etching process. Another disadvantage is that XeF2tends to be relatively expensive.

A MEMS fabrication method has now been developed that utilizes a heat vaporizable polymer as a sacrificial material. A heat vaporizable material is a solid material that vaporizes upon heating to a vaporization temperature, such that substantially all of the polymer (e.g., >95% by weight) is vaporized. The vaporization temperature range is preferably high enough such that the heat vaporizable material remains intact at normal fabrication temperatures, but low enough to avoid damaging other materials present during vaporization. In an embodiment, the heat vaporizable material is a heat vaporizable polymer. A variety of heat vaporizable polymers may be used. For example, one such heat vaporizable material is a heat-depolymerizable polycarbonate (HDP) such as poly(cyclohexene carbonate), an aliphatic polycarbonate that may be made from CO2and an epoxide, see U.S. Pat. No. 6,743,570 B2. Other HDP's may also be used.

Heat vaporization of a material, such as HDP, being used as a sacrificial material in a process for manufacturing interferometric modulators, such as process800illustrated inFIG. 8, may be advantageous as compared to removal of the sacrificial material using an etchant such as XeF2. In an embodiment, an advantage is that the vapors given off during heating of HDP are non-toxic or less toxic than vapors given off in an etching process. This simplifies the environmental requirements of the chamber being used for removing the sacrificial material. A simple oven, or even a heated surface such as a heated plate, may be used to heat substrates to a temperature sufficient for vaporization. Use of an oven or heated plate and, in one embodiment, simplified venting requirements afford an advantage of being able to process a substantially larger glass (or temperature resistant plastic) plate than the substrates provided for in etchers. Glass plates up to about 2 meters by about 3 meters, or larger, may be processed. This size of substrate would permit the manufacture of relatively large MEMS devices, e.g., large-screen-TV sized interferometric modulator arrays. In addition, non-uniformity produced by etching may be reduced by heating instead of etching.

The use of heat vaporization may permit the use of a wider array of materials including those materials that are etchable by XeF2. For example, one or more of various structures such as the electrically conductive layer, the substrate and the support structure may comprise a material that is etchable by xenon diflouride. In addition, use of etch stops (which may, in the fabrication of MEMS devices, complicate the process and increase costs) may be reduced or eliminated. The use of heat vaporization may also allow for process flexibility, which may result in the elimination of entire steps such as patterning.

FIG. 9is a flow diagram illustrating certain steps in an embodiment of a method of making a MEMS device. Such steps may be present in a process for manufacturing, e.g., interferometric modulators of the general type illustrated inFIGS. 1 and 7, along with other steps not shown inFIG. 9.FIGS. 10athrough10cschematically illustrate an embodiment of a method for fabricating a MEMS device. With reference toFIGS. 9 and 10, the process900begins at step905with the depositing of a polymer layer510over a substrate500as depicted inFIG. 10a. In one embodiment, the polymer is a heat vaporizable polymer such as an aliphatic polycarbonate, one example being poly(cyclohexene carbonate). Other heat-vaporizable polymers may be used including organic and inorganic polymers. The polymer serves as a sacrificial layer similar to the sacrificial layer formed in step810ofFIG. 8. The substrate500may comprise a material that is etchable by xenon diflouride. The deposition in step905may take many forms such as spin coating, extrusion coating, spray coating and printing. In one embodiment, inkjet deposition is used. In one embodiment, the heat vaporizable polymer is self planarizing. In one embodiment, the substrate500may comprise any transparent material such as glass or a heat resistant plastic that is not unduly affected by temperatures that bring about vaporization of the sacrificial polymer layer510. In another embodiment, the substrate500can comprise an optical stack16as inFIGS. 1 and 7.

The process900illustrated inFIG. 9continues at step910with the formation of an electrically conductive layer520over the polymer layer510as depicted inFIG. 10b. In one embodiment, the electrically conductive layer is part of the movable reflective layer14inFIGS. 1 and 7. Since the sacrificial polymer layer510is still present at step910of the process900, the movable reflective layer14is typically not movable at this stage. A partially fabricated MEMS device, e.g. a partially fabricated interferometric modulator, that contains the sacrificial polymer layer510may be referred to herein as an “unreleased” MEMS device. The electrically conductive layer520may comprise a metal (e.g. aluminum or aluminum alloy). Since process900uses vaporization, at step915, to remove the polymer layer510, materials that are etchable by XeF2may also be used for the electrically conductive layer. Such XeF2-etchable materials comprise titanium, tungsten and tantalum. Forming the electrically conductive layer520in step910may include one or more deposition steps as well as one or more patterning or masking steps.

Process900continues at step915with the vaporization of at least a portion of the heat vaporizable polymer layer510resulting in a cavity530as depicted inFIG. 10c. In one embodiment, the vaporizing step915comprises heating. Heating may be done on a heated plate, in an oven, in a kiln or by using any heating device capable of achieving and maintaining a temperature sufficient to vaporize the polymer for a long enough time that substantially all of the polymer vaporizes. In one embodiment, the heat vaporizable polymer is poly(cyclohexene carbonate) which vaporizes at about 300° C. Other heat vaporizable materials may be used. Materials that may be used include those that vaporize in temperature ranges high enough to be in a solid state during steps905and910and other steps not shown inFIG. 9, but vaporize at temperatures low enough such that other materials present during the vaporizing step915are not unduly affected. In one embodiment, materials present during step915include materials in the movable reflective layer14, materials in the optical stack16, materials in the substrate20and materials in the post18as shown inFIGS. 1 and 7. In one embodiment, a vaporization temperature range of about 200° C. to about 350° C. is acceptable. In this embodiment, deposition and patterning steps are preferably carried out at temperatures below the 200° C. vaporization temperature in order not to vaporize the polymer layer prematurely. In this embodiment, the 350° C. temperature may be about the maximum temperature that other materials, such as aluminum and indium tin oxide, can withstand without adverse effects. Adverse effects of heating may include hillocking, transmission and/or electrical resistance change. The heat vaporizable material should be a material that vaporizes within an acceptable temperature range and where substantially all (greater than about 95% by weight) of the heat vaporizable material is removed. Preferably, the heat vaporizable material vaporizes relatively quickly, e.g., within about 10 seconds to about 30 minutes, at the vaporization temperature.

In one embodiment a patterning step (not shown inFIGS. 9or10) may take place after step905and before the formation of the electrically conductive layer520in step910. This patterning may comprise techniques such as electron beam lithography and image transfer. The patterning may be done to form a support structure aperture in the polymer layer510. After the patterning, a depositing step (not shown inFIG. 9) may take place. A non-conductive material may be deposited into the support structure aperture formed in the patterning step to form a post18as shown inFIGS. 1 and 7. Step910may then form the electrically conductive layer520over the polymer layer510and over the post such that the post will support the electrically conductive-layer after removal of the polymer layer510in step915. In one embodiment, XeF2-etchable materials may be used in forming at least part of the post structure. XeF2-etchable materials suitable for the post structure include molybedenum and silicon-containing materials, such as silicon itself (including amorphous silicon, polysilicon, and crystalline silicon), as well as silicon germanium and silicon nitride. In some embodiments, the process900may include additional steps and the steps may be rearranged from the illustrations ofFIGS. 9 and 10.

FIGS. 11athrough11dschematically illustrate an embodiment of a method for fabricating a MEMS device. With reference toFIGS. 9 and 11, a depositing step (not shown inFIG. 9) forms post structures710on a substrate700. This depositing step takes place prior to depositing the polymer layer at step905. In one embodiment, a non-conductive material is deposited to form the post structures710. In one embodiment, XeF2-etchable materials may be used in forming at least part of the post structures710. XeF2-etchable materials suitable for the post structure include molybedenum and silicon-containing materials, such as silicon itself (including amorphous silicon, polysilicon, crystalline silicon), as well as silicon germanium and silicon nitride. In one embodiment, the substrate700may comprise any transparent material such as glass or a heat resistant plastic that is not unduly affected by temperatures that bring about vaporization of the heat vaporizable polymer layer. In another embodiment, the substrate700may comprise an optical stack16as inFIGS. 1 and 7. After depositing post structures710, process900continues to step905with the depositing of a polymer layer720next to the post structures710and over the substrate700as shown inFIG. 11b.

The process900continues at step910with the formation of an electrically conductive layer730over at least a portion of polymer layer720and post structures710as illustrated inFIG. 11c. In one embodiment, electrically conductive layer730is part of the movable reflective layer14as illustrated inFIGS. 1 and 7. Since the sacrificial polymer layer720is still present at step910of the process900, the movable reflective layer14is typically not movable at this stage. A partially fabricated MEMS device, e.g. a partially fabricated interferometric modulator, that contains the sacrificial polymer layer720may be referred to herein as an “unreleased” MEMS device. The electrically conductive layer730may comprise a metal (e.g. aluminum or aluminum alloy). Since the process900uses vaporization, at step915, to remove the polymer layer720, materials that are etchable by XeF2may also be used for the electrically conductive layer. Such XeF2-etchable materials comprise titanium, tungsten and tantalum. Forming the electrically conductive layer730in step910may include one or more deposition steps as well as one or more patterning or masking steps.

The process900continues at step915with the vaporization of the sacrificial polymer layer720resulting in a cavity740as illustrated inFIG. 11d. In one embodiment, the vaporizing step915comprises heating. Heating may be done on a heated plate or in an oven, kiln or any heating device capable of achieving and maintaining a temperature sufficient to vaporize the polymer for a long enough time that substantially all of the polymer vaporizes.FIG. 11ddepicts a MEMS device, e.g., an interferometric modulator, in a released state. In some embodiments, the process900may include additional steps and the steps may be rearranged from the illustrations ofFIGS. 9 and 11.

FIG. 12is a flow diagram illustrating certain steps in another embodiment of a method of making an interferometric modulator. Such steps may be present in a process for manufacturing, e.g., interferometric modulators of the general type illustrated inFIGS. 1 and 7, along with other steps not shown inFIG. 12.FIGS. 13athrough13eschematically illustrate an embodiment of a method for fabricating an interferometric modulator. With reference toFIGS. 12 and 13, the process1000begins at step1005with providing a substrate600as depicted inFIG. 13a. In one embodiment, the substrate600may comprise any transparent material such as glass or a heat resistant plastic that is not unduly affected by temperatures that bring about vaporization of a heat vaporizable sacrificial polymer. Process1000continues at step1010with the deposition of a first electrically conductive material610over at least a portion of the substrate600as depicted inFIG. 13a. The first electrically conductive material610can be part of the optical stack16depicted inFIGS. 1 and 7. In one embodiment the first electrically conductive layer comprises indium tin oxide. At step1015, a sacrificial layer620, comprising a heat vaporizable material, is deposited over at least a portion of the first electrically conductive material610as illustrated inFIG. 13b. The sacrificial layer620may be deposited by techniques such as spin coating, extrusion coating, spray coating and printing. The sacrificial layer620is deposited in thicknesses and locations to provide for a cavity of the desired size between the first electrically conductive layer and the second electrically conductive layer deposited in step1025. The sacrificial layer may be deposited in select locations by, e.g., printing techniques, one of which is inkjet deposition. In one embodiment the sacrificial layer is printed onto locations adjacent to post structure locations (already deposited post structures or to-be-deposited post structure locations).

The process1000continues at step1020with the deposition of an insulator over the substrate600and adjacent to the sacrificial material620(or adjacent to the location of a to-be-deposited sacrificial material) to form a support structure630as depicted inFIG. 13c. In one embodiment, step1020is performed before step1015(similar to the schematic illustration ofFIG. 11), thereby eliminating a patterning step (not shown inFIG. 10) to form a support post aperture. The insulator material may be used, in. an embodiment, to form support posts18inFIGS. 1 and 7. The insulator material may include materials etchable by XeF2as discussed above. Continuing at step1025, a second electrically conductive material640is deposited over at least a portion of the sacrificial material620as depicted inFIG. 13d. The second electrically conductive material640may be part of the movable reflective layer14ofFIGS. 1 and 7. The movable reflective layer14is configured such that the post structure supports the movable reflective layer including the second electrically conductive layer640.

After step1025, the partially fabricated interferometric modulater is in an unreleased state. In one embodiment, the unreleased interferometric modulator depicted inFIG. 13dincludes a first electrically conductive material610that is a partially reflective layer, a second electrically conductive material640that is a movable reflective layer, a sacrificial material620, the sacrificial material being removable by heat-vaporization to thereby form a cavity650, and the support structure630is a support post. The act of releasing the interferometric modulator is performed at step1030by vaporizing the sacrificial material620resulting in the cavity650as depicted inFIG. 13e. In one embodiment, vaporization is accomplished by heating the entire unreleased interferometric modulator to a temperature and for a duration sufficient to remove substantially all of the sacrificial material. After step1030, the interferometric modulator is in a released state. In some embodiments, the process1000may include additional steps and the steps may be rearranged from the illustrations ofFIGS. 12 and 13.

An embodiment of an unreleased interferometric modulator includes a first means for reflecting light, a second means for reflecting light, a first means for supporting the second reflecting means, and a second means for supporting the second reflecting means, where the first supporting means comprises a sacrificial material, the sacrificial material being removable by heat-vaporization to thereby form a cavity defined by the first reflecting means, the second reflecting means, and the second supporting means. With reference toFIG. 13d, aspects of this embodiment include where the first reflecting means is a partially reflective layer, such as the first electrically conductive material610, where the second reflecting means is a movable reflective layer such as the second electrically conductive material640, where the first supporting means is a sacrificial layer such as the sacrificial material620, and where the second supporting means is a support post such as the support structure630.

In one embodiment, the process900inFIG. 9and/or the process1000inFIG. 12may include a patterning step that comprises forming vent holes in the other materials, including, e.g., one or more of the substrates, the electrically conductive layers and/or any other structures present in the MEMS device or interferometric modulator. The vent holes, which may be similar to vent holes used in etching processes, serve as exit pathways for the vaporized sacrificial materials.

In an embodiment, vent holes are eliminated or reduced in number and/or size, and the sacrificial material, in this example a heat vaporizable polymer, escapes to the sides of the moveable reflective layer.

While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.