Electrode and interconnect materials for MEMS devices

A microelectromechanical (MEMS) device is presented which comprises a metallized semiconductor. The metallized semiconductor can be used for conductor applications because of its low resistivity, and for transistor applications because of its semiconductor properties. In addition, the metallized semiconductor can be tuned to have optical properties which allow it to be useful for optical MEMS devices.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems (MEMS). More specifically, the invention relates to MEMS devices having an electrical contact, electrode interconnect structures. One particular application can be found in capacitive MEMS devices. Finally, due to the (semi)-transparent nature of the electrode material in visible light, the invention also relates to optical MEMS devices, in general, and interferrometric light modulators in particular.

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 have 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 this type of device, one plate may be a stationary layer deposited on a substrate and the other plate may be a metallic membrane separated from the stationary layer by an air gap. 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 OF CERTAIN EMBODIMENTS

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.

One embodiment is a microelectromechanical system (MEMS) device, including a conducting electrode including a metallized semiconductor, and a movable element configured to be actuated by the conductor.

Another embodiment is a method of using a microelectromechanical system (MEMS) device, including applying a voltage to a conductor including a metallized semiconductor, where a movable element is actuated in response to the voltage.

Another embodiment is a method of manufacturing a microelectromechanical system (MEMS) device, the method including forming a conductor including a metallized semiconductor, and forming a movable element configured to be actuated by the conductor.

Another embodiment is a microelectromechanical system (MEMS) device, including means for actuating a MEMS element, where the actuating means is configured to partially transmit light and to partially reflect light.

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.

Embodiments of the invention relate to MEMS devices that include a conductor made of a metallized semiconductor material. In one embodiment, the MEMS device is an interferometric modulator with a transparent substrate, an electrode conductor and a movable mirror. Creating an electrical potential between the movable mirror and the electrode conductor results in movement of the movable mirror towards the electrode conductor. In one embodiment, the electrode conductor comprises a metallized semiconductor, such as a metal silicide, metal germanide or metal germosilicide. By using such materials, the absorber layer and conductor layer in a typical interferometric modulator can be combined into a single layer.

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. The partially reflective layer can be formed from a variety of materials that are partially reflective such as various metals, semiconductors, and dielectrics. Some examples of suitable materials include oxides, nitrides, and fluorides. Other examples include germanium (Ge), nickel silicide (NiSi), molybdenum (Mo), titanium (Ti), tantalum (Ta), and platinum (Pt). The partially reflective layer can be formed of one or more layers of materials, and each of the layers can be formed of a single material or a combination of materials.

In some embodiments, the layers of the optical stack 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 speaker44, an input device48, and a microphone46. 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 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 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 a 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 buffer28, and to an 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 antenna transmits and 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, 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 digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data.

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 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. Conditioning hardware52generally includes amplifiers and filters for transmitting signals to the speaker45, and for receiving signals from the microphone46. 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, driver controller29is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, array driver22is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a 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, 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, 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.

Power supply50can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply50is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply50is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, 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 supports18. InFIG. 7B, the moveable reflective layer14is attached to supports at the corners only, on tethers32. InFIG. 7C, the moveable 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 are herein referred to as support posts. The embodiment illustrated inFIG. 7Dhas 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 posts by filling holes between the deformable layer34and the optical stack16. Rather, the support posts are formed of 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 the portions of the interferometric modulator on the side of the reflective layer opposite the substrate20, including the deformable layer34. This allows the shielded areas to be configured and operated upon without negatively affecting the image quality. Such shielding allows the bus structure44inFIG. 7E, which provides the ability to separate the optical properties of the modulator from the electromechanical properties of the modulator, such as addressing and the movements that result from that addressing. 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.

FIGS. 8A and 8Bshow MEMS element818which operates as a switch. MEMS element818comprises insulator808, which is formed on substrate820and supports a portion of mechanical layer814. Electrode812is formed on substrate820so as to be spaced apart from mechanical layer814and is positioned between substrate820and mechanical layer814near a portion of mechanical layer814not supported by insulator808. MEMS element818also comprises terminal810formed on the substrate so as to be positioned between substrate820and mechanical layer814near the unsupported end of mechanical layer814.

Operation of the MEMS element is similar to that of the interferometric modulator MEMS element described above. An electrical potential between mechanical layer814and electrode812generates an electromotive force such that the mechanical layer814is attracted to electrode812. When the potential, and therefore attractive the electromotive force, is large enough, mechanical layer814deflects towards electrode812. Accordingly, the end of mechanical layer814approaches terminal810. When the deflection of mechanical layer814is sufficient, mechanical layer814contacts terminal810and an electrical connection is established between mechanical layer814and terminal810.

After the electrical connection is established a signal driven onto mechanical layer814will be transmitted to terminal810. Alternatively, after the electrical connection is established, a signal driven onto terminal810will similarly be transmitted to mechanical layer814.

Once the electrical connection between mechanical layer814and terminal810is no longer needed, the electric potential between mechanical layer814and terminal810may be reduced until the mechanical restorative force of mechanical layer814is greater than the attractive electromotive force between mechanical layer814and terminal810. In response to the greater restorative force, the mechanical layer814returns towards a mechanically relaxed position not contacting terminal810. The electrical connection is broken and the switch is again open and non-conductive.

Electrode812and terminal810may comprise one or more metallized semiconductor materials such as, but not limited to, a metal silicide, a metal germanide, and a metal germosilicide (e.g. NiSi, CoSi2, MoSi, CoSi, TaSi, TiSi, and Ni(Six-1Gex)) in different crystalline phases and compositions. Metallized semiconductor materials comprise a metal and a semiconductor material such as, but not limited to silicon, germanium, gallium arsenide, Six-1Gex, alloys, and SiC. A benefit of metallized semiconductors is shown inFIG. 8B, which illustrates MEMS both element818ofFIG. 8Aand transistor840on substrate820. Transistor840comprises gate electrode837, gate oxide835, drain electrode831, channel region832, and source electrode833. Transistor840may be configured to directly or indirectly drive MEMS element818, or may be configured to directly or indirectly sense a state of MEMS element818. The material used for electrode812and/or terminal810may be similar to or substantially identical to that used for drain electrode831, channel region832, and source electrode833. In some embodiments, electrode812, drain electrode831, channel region832, and source electrode833are formed in substantially the same processing steps.

FIGS. 9A through 9Dare cross-sections of the MEMS element818and transistor840at various stages in a manufacturing process. The following description is directed towards use of a semiconductor material. Such semiconductor materials include materials which comprise, for example, at least one of silicon, germanium, and gallium arsenide. These and various other materials with appropriate semiconductor and conductor properties may be used.FIG. 9Ashows substrate920and semiconductor layer950formed on substrate920. At this point in the manufacturing process, semiconductor layer950may not substantially comprise metal.FIG. 9Bshows semiconductor layer950after processing such that it is formed into electrode semiconductor902, terminal semiconductor900, and transistor semiconductor930. Transistor gate oxide935and transistor gate937are then formed over transistor semiconductor930, as shown inFIG. 9C. A metal is subsequently deposited over substrate920. The metal may comprise at least one of nickel, molybdenum, cobalt, tantalum, and titanium. Other metals may also be used. During a subsequent annealing process typically at 300-900° C., some of the deposited metal integrates into the structure of the underlying electrode semiconductor902, terminal semiconductor900, and transistor semiconductor930. The resulting material is advantageous for use both as a conductor, such as electrode912and terminal910, and as transistor electrodes, such as gate electrode937, drain electrode933, and source electrode931, as shown inFIG. 9C.FIG. 9Dshows insulator908and mechanical layer914fabricated by subsequent processing, so as to complete MEMS element918.

As indicated above, a portion of both a transistor and a MEMS element may be substantially simultaneously fabricated. Because metallized semiconductor materials are useful for both conductor applications and transistor electrode and channel applications, such simultaneous fabrication of different portions of a MEMS device is especially advantageous, as these integrated devices can be provided with reduced manufacturing complexity, size, and cost.

Another characteristic of metallized semiconductors is that, in addition to electrical and semiconductor properties, they have optical reflectance properties which allow for advantageous use in optical MEMS devices, such as interferometric modulator1000, shown inFIG. 10. While the following discussion is directed toward interferometric modulator1000, the aspects described herein are not limited to this interferometric modulator embodiment, and can be applied to any number of other interferometric modulator embodiments, as well as any other optical MEMS device. Interferometric modulator1000ofFIG. 10is similar in structure and function to the interferometric modulators shown inFIGS. 7C-7E. Interferometric modulator1000comprises electrode1016formed on substrate1020, insulator1018formed on electrode1016, and reflective layer1014supported by deformable mechanical layer1134formed above insulator1018. Interferometric cavity1010is formed between electrode1016and reflective layer1014. As described above, light λ is introduced to interferometric cavity1010through substrate1020, electrode1016, and insulator1018. Light of color and intensity depending on interferometric properties of interferometric cavity1016is reflected back through insulator1018, electrode1016, and substrate1020. Accordingly, the optical properties and the electrical properties of electrode1016both affect the performance of interferometric modulator1000.

Specifically, at least optical reflectance and electrical resistivity are parameters affecting the performance of interferometric modulator1000. Electrode1016provides an electrical function by serving as a conductor functioning to affect the position of reflective layer1014so as to adjust a primary dimension of interferometric cavity1010, as described above. In addition, electrode1016provides an optical function by serving as a partially reflective layer, which defines a first major boundary of interferometric cavity1010, the other major boundary being defined by the reflective layer1014. In some interferometric modulators, these two functions, electrical and optical, are provided by two separate layers. For example, transparent ITO (or other transparent conductive oxide, e.g. ZnO) may be used as the conductor functioning to affect the position of the reflective layer, and Cr may be used as a partially reflective layer, or absorber, defining a first major boundary of the interferometric cavity. However, in embodiments of this invention, a metallized semiconductor layer is used to combine and perform the functions of the ITO and Cr layers. Another benefit of using a metallized semiconductor for the electrode/absorber is that the resistivity of metallized semiconductor materials is lower than the resistivity of ITO, as is shown in the following table:

Accordingly, use of a metallized semiconductor allows for production of thinner electrodes, while maintaining a desired low resistance. For example NiSi can be used to form an electrode which is from about 100 Å to about 500 Å. A MoSi electrode can be from about 200 Å to about 1000 Å. A CoSi electrode can be from about 50 Å to about 200 Å, a TaSi electrode can be from about 80 Å to about 350 Å, and a TiSi electrode can be from about 50 Å to about 200 Å.

The electrical and optical properties of the single metallized semiconductor layer can be tuned by the specific material used for the metallized semiconductor layer and by the thickness of the metallized semiconductor layer, its composition, crystalline phases and dopants. For example, given two metallized semiconductor layers of the same material and different thicknesses, the thicker layer will have less electrical sheet resistance (Ω/□) and greater optical reflectance in comparison to the thinner layer.

Additionally, given two metallized semiconductor layers of the same thickness and different materials, one will have greater optical reflectance than the other and one will have greater electrical sheet resistance (Ω/□) than the other, according to the physical properties of the individual metallized semiconductor materials. Accordingly, by intelligent selection of material and thickness of the metallized semiconductor layer, the electrical and optical properties can be tuned to desired values. The following table shows resistivity (μΩcm) of various metallized semiconductor materials.

In addition, other processing parameters, such as, but not limited to, doping concentration, annealing temperature, and annealing time can be used to tune the electrical and optical properties of the metallized semiconductor layer.

In addition to a single metallized semiconductor layer providing both electrical and optical functions, an advantageous aspect of using a metallized semiconductor layer for the electrode/absorber is that semiconductor based electronic devices (e.g. transistors, capacitors, memory devices, and microprocessors) can be manufactured using some of the same processing steps as the interferometric modulator integrated on the same substrate.

FIGS. 11A through 11Cshow a manufacturing process that can be used to simultaneously manufacture a MEMS element1100and transistor1140.FIGS. 11A through 11Care cross-sections of the interferometric modulator1000and transistor1140at various stages in a manufacturing process. The following description is directed towards use of a semiconductor material. For example materials which comprise at least one of silicon, germanium, and gallium arsenide may be used. However, any material with appropriate semiconductor and conductor properties may be used.FIG. 11Ashows substrate1120and semiconductor layer1150formed on substrate1120. At this point in the manufacturing process semiconductor layer1150may not substantially comprise metal.FIG. 11Bshows semiconductor layer1150after processing such that semiconductor layer1150is formed into electrode semiconductor1106and transistor semiconductor1130. Transistor gate oxide1135and transistor gate1137are subsequently formed over transistor semiconductor1130. A metal is subsequently deposited over substrate1120. The metal may comprise at least one of nickel, molybdenum, cobalt, tantalum, and titanium. Other metals may also be used. During a subsequent annealing process, some of the metal integrates into the structure of the underlying electrode semiconductor1106and transistor semiconductor1130. The resulting material is advantageous for use both as a conductor, such as electrode1116and as transistor electrodes, such as gate electrode1137, drain electrode1133, and source electrode1131, as is shown inFIG. 11C.FIG. 11Calso shows insulator1118, reflective layer1114, and mechanical layer1134fabricated by subsequent processing, so as to complete interferometric modulator1100.

As indicated, a portion of both a transistor and an interferometric modulator may be substantially simultaneously fabricated. Because metallized semiconductor materials are useful for optical applications, conductor applications and transistor electrode applications, such simultaneous fabrication of different portions of an optical MEMS device is especially advantageous, as these various applications can be provided with reduced manufacturing complexity, cost and device size.

In order to implement the simultaneous processing of a transistor and a MEMS element, such as those discussed above, the transistor and the MEMS element may be may be manufactured or partially manufactured on a thin film transistor (TFT) or semiconductor production line.

TFT's are transistors in which the drain, source, and channel region of the transistor are formed by depositing a semiconductor over a base substrate. The semiconductor is appropriately patterned so as to define the drain, source, and channel regions. Typically, the base substrate is a non-semiconductor substrate. See, e.g., “Thin Film Transistors—Materials and Processes—Volume 1 Amorphous Silicon Thin Film Transistors,” ed. Yue Kuo, Kluwer Academic Publishers, Boston (2004). The base substrate over which the TFT is formed may be a non-semiconductor such as glass, plastic or metal. The semiconductor that is deposited to form the channel region of the TFT may, for example, comprise silicon (e.g., a-Si, a-SiH) and/or germanium (e.g., a-Ge, a-GeH), and/or gallium arsenide (e.g., a-GaAs), and may also comprise dopants such as phosphorous, arsenic, antimony, and indium.

Certain MEMS devices may be at least partially processed on a TFT production line simultaneously with certain TFT layers. For example, the MEMS device shown inFIG. 8B, comprising MEMS element818and transistor840, may be fabricated according to the process described with reference toFIGS. 9A through 9D, where at least some of the fabrication is performed on a TFT production line. For example, the processing aspects described with reference toFIGS. 9A through 9Cmay occur on a TFT production line, while the formation of insulator908and mechanical layer914may be performed on a second production line. In some embodiments, the TFT production line may be modified so as to be additionally capable of performing these fabrication steps.

An interferometric modulator comprising ITO as an electrode and Cr as an absorber and an interferometric modulator comprising NiSi as a combined electrode/absorber were each simulated. Certain layers and layer thicknesses and optical performance simulation results are shown in the following table:

FIGS. 12A and 12Bshow the reflectance of each of the simulated interferometric modulators across wavelengths of visible light. ComparingFIGS. 12A and 12Bshows that the interferometric modulator with the metallized semiconductor has better optical performance at least because it has higher reflectance across almost the entire band in the bright state, and has lower reflectance across almost the entire band in the dark state.

While the above detailed description has shown, described, and pointed out novel features 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.