Patent Application
20130307857
This disclosure relates to piezo-electric layers and more particularly to piezo-electric layers that can mitigate stiction in electromechanical systems.
Electromechanical systems include devices having electrical and mechanical elements, actuators, transducers, sensors, optical components (for example, mirrors) and electronics. Electromechanical systems can be manufactured at a variety of scales including, but not limited to, microscales and nanoscales. For example, microelectromechanical systems (MEMS) devices can include structures having sizes ranging from about a micron to hundreds of microns or more. Nanoelectromechanical systems (NEMS) devices can include structures having sizes smaller than a micron including, for example, sizes smaller than several hundred nanometers. Electromechanical elements may be created using deposition, etching, lithography, 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 electromechanical systems device is called an interferometric modulator (IMOD). 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 some implementations, an interferometric modulator may include a pair of conductive plates, one or both of which may be transparent and/or reflective, wholly or in part, and capable of relative motion upon application of an appropriate electrical signal. In an implementation, one plate may include a stationary layer deposited on a substrate and the other plate may include a reflective 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. Interferometric modulator devices have a wide range of applications, and are anticipated to be used in improving existing products and creating new products, especially those with display capabilities.
Various surfaces of the electromechanical systems (for example, a surface of the reflective membrane) can unintentionally adhere when mechanical restoring forces are unable to overcome surface adhesion forces such as capillary and electrostatic, van der Waals forces, the Casimir effect, and other kinds of attraction forces. This unintentional adhesion is referred to as “stiction.” Stiction in electromechanical systems can be of two types: (i) release related stiction; and (ii) in-use stiction. Release related stiction occurs during the process of “release” of the layers (for example, sacrificial layer removal) during fabrication of the electromechanical system. Surfaces of released electromechanical systems can adhere together upon contact during operation of the electromechanical system, and such adhesion can be referred to as “in-use stiction.” Various engineering methods such as surface engineering and surface coating have been proposed to reduce stiction in electromechanical systems.
The systems, methods and devices of the disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.
One innovative aspect of the subject matter described in this disclosure can be implemented in an electromechanical systems device, comprising an optical stack, a movable layer, and a piezo-electric layer. The movable layer is disposed over the optical stack and separated from the optical stack by a gap. The movable layer includes a deformable region that deforms when the movable layer is actuated. The movable layer further includes an optically active region that is positioned substantially flat when the movable layer is actuated. The movable layer is configured to actuate between at least a first position that is farther from the optical stack and a second position that is closer to the optical stack by the application of a first voltage across the optical stack and the movable layer. The deformable region of the movable layer is in an un-deformed state in the first position and in a deformed state in the second position. The piezo-electric layer is disposed over at least a portion of the deformable region of the movable layer. The piezoelectric layer is configured to provide a restorative force to restore the movable layer from the second position to the first position upon application of a second voltage across a first electrical contact and a second electrical contact of the piezoelectric layer.
In various implementations of the electromechanical systems device, the movable layer can include a first electrode layer that includes the first electrical contact. The electromechanical systems device can include a second electrode layer that includes the second electrical contact. In various implementations, the piezo-electric layer can be disposed between the movable layer and the second electrode. In various implementations, the first electrode layer can include a first portion including the first electrode contact and a second portion that includes the second electrical contact. In such implementations, the piezo-electric layer can extend between the first and second electrical contacts of the first electrode layer. In various implementations, the second voltage can be applied across the first and second electrode layers. In various implementations, the second voltage can be applied across the first and second electrical contacts of the first electrode layer.
In various implementations, the piezo-electric layer is configured such that a magnitude of the restorative force depends at least in part on the magnitude and/or the polarity of the second voltage. In various implementations, the magnitude of the second voltage can be between 0V and 40V. The second voltage can be an alternating current (AC) signal. In various implementations, a frequency of the AC signal can be proportional to the resonance frequency of the movable layer and/or the piezo-electric layer. In various implementations, the first electrical contact can be connected to an electrical ground via a first electrical switch and the second electrical contact can be connected to the electrical ground via a second electrical switch. In various implementations, the first and the second electrical switches can be periodically toggled to provide the restorative force. In various implementations, the first and the second electrical contacts can be connected together via an electrical switch which can be periodically toggled to short the first and second electrical contacts to provide the restorative force.
In various implementations, the movable layer can include a partially reflective layer. In various implementations, the movable layer, the optical stack and the gap can form an interferometric modulator. In various implementations, the device can be a reflective display element. In various implementations, the device can include at least one support structure that is configured to support the movable layer over the optical stack. The non-deformable region of the movable layer can be disposed over the support structure.
Another innovative aspect of the subject matter described in this disclosure can be implemented in an electromechanical systems device comprising means for partially transmitting light, a movable means for reflecting light and a means for producing mechanical strain. The movable light reflecting means is disposed over the partially light transmitting means and separated from the partially light transmitting means by a gap. The movable light reflecting means includes a deformable region that deforms when the movable light reflecting means is actuated. The movable light reflecting means includes an optically active region that is substantially flat when the movable light reflecting means is actuated. The movable light reflecting means is configured to actuate between at least a first position that is farther from the partially light transmitting means and a second position that is closer to the partially light transmitting means by the application of a first voltage between the partially light transmitting means and the movable reflecting means. The deformable region of the movable reflecting means is in an un-deformed state in the first position and in a deformed state in the second position. The mechanical strain producing means is disposed over at least a part of the deformable region of the movable light reflecting means. The mechanical strain producing means is configured to generate a mechanical restorative force to restore the movable light reflecting means from the second position to the first position upon application of a second voltage across a first electrical contact and a second electrical contact of the mechanical strain producing means.
In various implementations of the device, the fixed means for partially transmitting light can include an optical stack having a partially transmissive layer. In various implementations, the movable means for reflecting light can include a movable reflecting layer. In various implementations, the mechanical strain producing means can include a piezo-electric layer. In various implementations, the movable means for reflecting light can include a first electrode layer that includes the first electrical contact. Various implementations of the device can further include a second electrode layer such that the mechanical strain producing means is disposed between the movable light reflecting means and the second electrode. In various implementations of the device, the first electrode layer can include a first portion including the first electrical contact and a second portion including the second electrical contact, and the mechanical strain producing means can extend between the first and second portions of the first electrode layer.
Another innovative aspect of the subject matter described in this disclosure can be implemented in a method of manufacturing an electromechanical systems device. The method includes providing a substrate. The method further includes forming a stack that is partially transmissive to light over the substrate. The method further includes forming a movable layer over the stack. The movable layer is separated from the stack by a gap. Forming the movable layer includes forming a deformable region that deforms when the movable layer is actuated and forming an optically active region that is positioned substantially flat when the movable layer is actuated. The movable layer is configured to actuate between at least a first position that is farther from the fixed stack and a second position that is closer to the fixed stack by the application of a first voltage between the fixed stack and the movable layer. The deformable region of the movable layer is in an un-deformed state in the first position and in a deformed state in the second position. The method further includes forming a piezo-electric layer over at least part of the deformable region of the movable layer. The piezoelectric layer is configured to provide a restorative mechanical force to restore the movable layer from the second position to the first position upon application of a second voltage across a first electrical contact and a second electrical contact of the piezoelectric layer.
In various implementations of the method, forming the movable layer can include forming a first electrode that includes the first electrical contact. In various implementations, forming the first electrode can include patterning the first electrode to have a first portion and a second portion. The first and second portions can be separated from each other by an opening. The piezo-electric layer can be formed such that a portion of the piezo-electric layer extends into the opening. The method can further include forming a second electrode layer over the piezo-electric layer.
Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.
Like reference numbers and designations in the various drawings indicate like elements.
The following detailed description is directed to certain implementations for the purposes of describing the innovative aspects. However, the teachings herein can be applied in a multitude of different ways. The described implementations may be implemented in any device that is configured to display an image, whether in motion (for example, video) or stationary (for example, still image), and whether textual, graphical or pictorial. More particularly, it is contemplated that the implementations may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, facsimile devices, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), computer monitors, auto displays (for example, odometer display, etc.), cockpit controls and/or displays, camera view displays (for example, display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, microwaves, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washers, dryers, washer/dryers, parking meters, packaging (for example, MEMS and non-MEMS), aesthetic structures (for example, display of images on a piece of jewelry) and a variety of electromechanical systems devices. The teachings herein also can be used in non-display applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion-sensing devices, magnetometers, inertial components for consumer electronics, parts of consumer electronics products, varactors, liquid crystal devices, electrophoretic devices, drive schemes, manufacturing processes, and electronic test equipment. Thus, the teachings are not intended to be limited to the implementations depicted solely in the Figures, but instead have wide applicability as will be readily apparent to a person having ordinary skill in the art.
The electromechanical systems devices can include an array of interferometric modulators (IMODs). An interferometric modulator referred to herein can be configured as a bi-stable electromechanical device or an analog electromechanical device (sometimes referred to specifically as an “AIMOD”). Implementations of IMODs described herein can include an optical stack that is at least partially transmissive to light in the visible spectral range, a movable layer and a piezo-electric layer both disposed over the optical stack. The movable layer includes an optically active region that is at least partially reflective to light in the visible spectral range. The optically active portion of the movable layer includes a deformable region that can be actuated between a first position that is further from the optical stack and a second position that is closer to the optical stack by the application of an actuating force. The movable layer is in an un-deformed state in the first position and in a deformed state in the second position. The piezo-electric layer is disposed over at least a portion of the deformable region of the movable layer. The piezo-electric layer provides a restorative electro-mechanical force upon the application of a voltage across the piezo-electric layer that can restore the deformable region of the movable layer to the un-deformed state in the absence of the actuation force. The voltage applied across the piezo-electric layer can be a pulse of alternating current (AC) voltage. The frequency of the AC voltage pulse can be proportional to a resonance frequency of the movable layer.
Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. Disposing a piezo-electric layer over at least a portion of the deformable region of the movable layer in various implementations of IMODs can reduce or mitigate release related stiction of the movable layer during the fabrication of the IMODs which can advantageously increase yield of the IMODs. Additionally, the piezo-electric layer disposed over at least a portion of the deformable region of the movable layer can reduce or mitigate stiction of the movable layer during operation of the IMODs, which can increase the lifetime and/or the performance of devices including such implementations of IMODs.
An example of a suitable MEMS device, to which the described implementations may apply, is a reflective display device. Reflective display devices can incorporate interferometric modulators (IMODs) to selectively absorb and/or reflect light incident thereon using principles of optical interference. IMODs can include an absorber, a reflector that is movable with respect to the absorber, and an optical resonant cavity defined between the absorber and the reflector. The reflector can be moved to two or more different positions, which can change the size of the optical resonant cavity and thereby affect the reflectance of the interferometric modulator. The reflectance spectrums of IMODs can create fairly broad spectral bands which can be shifted across the visible wavelengths to generate different colors. The position of the spectral band can be adjusted by changing the thickness of the optical resonant cavity, that is, by changing the position of the reflector.
The IMOD display device can include a row/column array of IMODs. Each IMOD can include a pair of reflective layers, i.e., a movable reflective layer and a fixed partially reflective layer, positioned at a variable and controllable distance from each other to form an air gap (also referred to as an optical gap or cavity). The movable reflective layer may be moved between at least two positions. In a first position, i.e., a relaxed position, the movable reflective layer can be positioned at a relatively large distance from the fixed partially reflective layer. In a second position, i.e., an actuated position, the movable reflective layer can be positioned more closely to the partially reflective layer. Incident light that reflects from the two layers can interfere constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel. In some implementations, the IMOD may be in a reflective state when unactuated, reflecting light within the visible spectrum, and may be in a dark state when actuated, reflecting light outside of the visible range (e.g., infrared light). In some other implementations, however, an IMOD may be in a dark state when unactuated, and in a reflective state when actuated. In some implementations, the introduction of an applied voltage can drive the pixels to change states. In some other implementations, an applied charge can drive the pixels to change states.
The depicted portion of the pixel array in
In
The optical stack 16 can include a single layer or several layers. The layer(s) can include one or more of an electrode layer, a partially reflective and partially transmissive layer and a transparent dielectric layer. In some implementations, the optical stack 16 is 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 substrate 20. The electrode layer can be formed from a variety of materials, such as various metals, for example indium tin oxide (ITO). The partially reflective layer can be formed from a variety of materials that are partially reflective, such as various metals, e.g., chromium (Cr), semiconductors, and dielectrics. 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 implementations, the optical stack 16 can include a single semi-transparent thickness of metal or semiconductor which serves as both an optical absorber and conductor, while different, more conductive layers or portions (for example, of the optical stack 16 or of other structures of the IMOD) can serve to bus signals between IMOD pixels. The optical stack 16 also can include one or more insulating or dielectric layers covering one or more conductive layers or a conductive/absorptive layer.
In some implementations, the layer(s) of the optical stack 16 can be patterned into parallel strips, and may form row electrodes in a display device as described further below. As will be understood by one having skill in the art, the term “patterned” is used herein to refer to masking as well as etching processes. In some implementations, a highly conductive and reflective material, such as aluminum (Al), may be used for the movable reflective layer 14, and these strips may form column electrodes in a display device. The movable reflective layer 14 may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of the optical stack 16) to form columns deposited on top of posts 18 and an intervening sacrificial material deposited between the posts 18. When the sacrificial material is etched away, a defined gap 19, or optical cavity, can be formed between the movable reflective layer 14 and the optical stack 16. In some implementations, the spacing between posts 18 may be approximately 1-1000 um, while the gap 19 may be less than 10,000 Angstroms (Å).
In some implementations, each pixel of the IMOD, whether in the actuated or relaxed state, is essentially a capacitor formed by the fixed and moving reflective layers. When no voltage is applied, the movable reflective layer 14 remains in a mechanically relaxed state, as illustrated by the pixel 12 on the left in
The processor 21 can be configured to communicate with an array driver 22. The array driver 22 can include a row driver circuit 24 and a column driver circuit 26 that provide signals to, e.g., a display array or panel 30. The cross section of the IMOD display device illustrated in
In some implementations, a frame of an image may be created by applying data signals in the form of “segment” voltages along the set of column electrodes, in accordance with the desired change (if any) to the state of the pixels in a given row. Each row of the array can be addressed in turn, such that the frame is written one row at a time. To write the desired data to the pixels in a first row, segment voltages corresponding to the desired state of the pixels in the first row can be applied on the column electrodes, and a first row pulse in the form of a specific “common” voltage or signal can be applied to the first row electrode. The set of segment voltages can then be changed to correspond to the desired change (if any) to the state of the pixels in the second row, and a second common voltage can be applied to the second row electrode. In some implementations, the pixels in the first row are unaffected by the change in the segment voltages applied along the column electrodes, and remain in the state they were set to during the first common voltage row pulse. This process may be repeated for the entire series of rows, or alternatively, columns, in a sequential fashion to produce the image frame. The frames can be refreshed and/or updated with new image data by continually repeating this process at some desired number of frames per second.
The combination of segment and common signals applied across each pixel (that is, the potential difference across each pixel) determines the resulting state of each pixel.
As illustrated in
When a hold voltage is applied on a common line, such as a high hold voltage VCHOLD
When an addressing, or actuation, voltage is applied on a common line, such as a high addressing voltage VCADD
In some implementations, hold voltages, address voltages, and segment voltages may be used which always produce the same polarity potential difference across the modulators. In some other implementations, signals can be used which alternate the polarity of the potential difference of the modulators. Alternation of the polarity across the modulators (that is, alternation of the polarity of write procedures) may reduce or inhibit charge accumulation which could occur after repeated write operations of a single polarity.
During the first line time 60a: a release voltage 70 is applied on common line 1; the voltage applied on common line 2 begins at a high hold voltage 72 and moves to a release voltage 70; and a low hold voltage 76 is applied along common line 3. Thus, the modulators (common 1, segment 1), (1,2) and (1,3) along common line 1 remain in a relaxed, or unactuated, state for the duration of the first line time 60a, the modulators (2,1), (2,2) and (2,3) along common line 2 will move to a relaxed state, and the modulators (3,1), (3,2) and (3,3) along common line 3 will remain in their previous state. With reference to
During the second line time 60b, the voltage on common line 1 moves to a high hold voltage 72, and all modulators along common line 1 remain in a relaxed state regardless of the segment voltage applied because no addressing, or actuation, voltage was applied on the common line 1. The modulators along common line 2 remain in a relaxed state due to the application of the release voltage 70, and the modulators (3,1), (3,2) and (3,3) along common line 3 will relax when the voltage along common line 3 moves to a release voltage 70.
During the third line time 60c, common line 1 is addressed by applying a high address voltage 74 on common line 1. Because a low segment voltage 64 is applied along segment lines 1 and 2 during the application of this address voltage, the pixel voltage across modulators (1,1) and (1,2) is greater than the high end of the positive stability window (i.e., the voltage differential exceeded a predefined threshold) of the modulators, and the modulators (1,1) and (1,2) are actuated. Conversely, because a high segment voltage 62 is applied along segment line 3, the pixel voltage across modulator (1,3) is less than that of modulators (1,1) and (1,2), and remains within the positive stability window of the modulator; modulator (1,3) thus remains relaxed. Also during line time 60c, the voltage along common line 2 decreases to a low hold voltage 76, and the voltage along common line 3 remains at a release voltage 70, leaving the modulators along common lines 2 and 3 in a relaxed position.
During the fourth line time 60d, the voltage on common line 1 returns to a high hold voltage 72, leaving the modulators along common line 1 in their respective addressed states. The voltage on common line 2 is decreased to a low address voltage 78. Because a high segment voltage 62 is applied along segment line 2, the pixel voltage across modulator (2,2) is below the lower end of the negative stability window of the modulator, causing the modulator (2,2) to actuate. Conversely, because a low segment voltage 64 is applied along segment lines 1 and 3, the modulators (2,1) and (2,3) remain in a relaxed position. The voltage on common line 3 increases to a high hold voltage 72, leaving the modulators along common line 3 in a relaxed state.
Finally, during the fifth line time 60e, the voltage on common line 1 remains at high hold voltage 72, and the voltage on common line 2 remains at a low hold voltage 76, leaving the modulators along common lines 1 and 2 in their respective addressed states. The voltage on common line 3 increases to a high address voltage 74 to address the modulators along common line 3. As a low segment voltage 64 is applied on segment lines 2 and 3, the modulators (3,2) and (3,3) actuate, while the high segment voltage 62 applied along segment line 1 causes modulator (3,1) to remain in a relaxed position. Thus, at the end of the fifth line time 60e, the 3×3 pixel array is in the state shown in
In the timing diagram of
The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example,
As illustrated in
In implementations such as those shown in
The process 80 continues at block 84 with the formation of a sacrificial layer 25 over the optical stack 16. The sacrificial layer 25 is later removed (e.g., at block 90) to form the cavity 19 and thus the sacrificial layer 25 is not shown in the resulting interferometric modulators 12 illustrated in
The process 80 continues at block 86 with the formation of a support structure e.g., a post 18 as illustrated in
The process 80 continues at block 88 with the formation of a movable reflective layer or membrane such as the movable reflective layer 14 illustrated in
The process 80 continues at block 90 with the formation of a cavity, e.g., cavity 19 as illustrated in
In various implementations of electromechanical systems (for example, the IMOD 12 illustrated in
The piezo-electric layer 915 is disposed over at least a portion of the deformable region of the movable layer 910. In some implementations, the piezo-electric layer 915 is disposed such that it overlaps with most of the deformable region of the movable layer 910. In various implementations, the piezo-electric layer 915 includes one or more piezo-electric material such as, for example, Aluminum nitride (AlN), Zinc oxide (ZnO) or low temperature lead zirconate titanate (PZT). The piezo-electric layer 915 can include materials that can be integrated with electromechanical systems device/integrated circuit fabrication process. In various implementations, the piezo-electric layer 915 can have a thickness between approximately 100 nm and 1000 nm. The thickness of the piezo-electric layer can depend on the material from which it is formed. For example, if the piezo-electric layer 915 includes AlN, the thickness of the piezo-electric layer 915 can be a few hundred nanometers. Although, in the implementations illustrated in
In various implementations, including the implementation depicted in
In some implementations, as depicted in
The piezo-electric layer 915 can be deposited over the movable layer 910 by using methods including, but not limited to, In PVD, PECVD, thermal CVD or spin-coating. The piezo-electric layer 915 can be deposited over the movable layer 910 during fabrication of the electromechanical systems device. For example, in implementations of electromechanical systems including an IMOD, the piezo-electric layer 915 can be deposited over the movable reflective layer after block 88 of the process 80 (
The piezo-electric layer 915 can accumulate electrical charges in response to a mechanical deformation. This phenomenon is referred to as direct piezo-electric effect. Conversely, the piezo-electric layer 915 can exhibit mechanical deformation in response to an applied Z-electric field. This phenomenon is referred to as reverse piezo-electric effect. Mathematically, piezo-electric effect can be described by Equation (1):
T
λ=σλv·Sv+eiλ·Ei (1)
In Equation (1) above, Tλ is the stress tensor of the piezo-electric layer 915. In various implementations, the stress tensor Tλ can be related to the restoration force produced by the piezo-electric layer 915. The term Sv in Equation (1) is the strain tensor of the piezo-electric layer 915. In various implementations, the strain tensor Sv can be related to deformation produced in the piezo-electric layer 915. The term σλv is the stiffness tensor of the piezo-electric layer 915 and the term eiλ is the piezo-electric coefficient tensor of the piezo-electric layer 915. The term Ei refers to the electric field generated in the piezo-electric layer 915.
The piezo-electric coefficient tensor eiλ of the piezo-electric layer 915 is a property of the material of the piezo-electric layer 915 and is different for different materials. For example, for aluminum nitride (AlN) the piezo-electric coefficient tensor eiλ is given by Equation (2):
Non-zero values for the elements in the third row and first column, e31, and the third row and second column, e32, of the tensor eiλ in Equation (2) indicates that if an electric field having a component along the vertical or z-direction (for example, along a direction perpendicular to the plane of the piezo-electric layer 915) is applied, the piezo-electric layer 915 can respond with a structural deformation (for example by expanding, contracting and/or rotating) in the plane of the piezo-electric layer 915 (for example, along the X and Y directions). Non-zero value for the element in the third row and third column, e33, of the tensor eiλ in Equation (2) indicates that the piezo-electric layer 915 can also deform (for example, by expanding, contracting and/or rotating) along a vertical direction (for example, along the Z direction) in response to an applied electric field.
Direct and reverse piezo-electric effect induced in the piezo-electric layer 915 can be used to mitigate or reduce release related or in-use stiction in the electromechanical systems device 900 as discussed below. To reduce or mitigate release related stiction, the piezo-electric layer 915 is deposited over the movable layer 910 prior to the removal of the sacrificial layer and the electromechanical systems device 900 is in the unreleased state as discussed above. The movable layer 910 is not free to move in the unreleased state of the electromechanical systems device. When the sacrificial layer is removed, the electromechanical systems device 900 is in the released state and the movable layer 910 becomes free to move. Upon removal of the sacrificial layer (“release”), the movable layer 910 can deform due to mechanical stresses in the material, which in turn deforms the piezo-electric layer 915. Deformation of the piezo-electric layer 915 during release or during operation of the electromechanical systems device 900 can cause charges to accumulate on the piezo-electric layer 915 due to a piezo-electric effect, which in turn can cause a voltage to be developed across the piezo-electric layer 915.
The deformed piezo-electric layer 915 can be returned to the un-deformed state by the application of a voltage that is equal in magnitude and opposite in polarity to the voltage developed across the deformed edges of the piezo-electric layer 915. In various implementations, the magnitude of the applied voltage can be between approximately 0V and 40V. In various implementations, the piezo-electric layer 915 can be returned to the un-deformed state by connecting the deformed edges to a ground as shown in
During the operation of such electromechanical systems, initially, the movable layer 910 is in the un-deformed state and in a first position that is farther from the stack 901. When an actuating force (for example, a potential difference applied between the movable layer 901 and the stack 901) is provided to the movable layer 910, the movable layer 910 is moved to a second position that is closer to the stack 901. In the second position the movable layer 910 is in the deformed state. When the actuating force provided to the movable layer 910 is removed, the movable layer 910 returns to the first position (and to the un-deformed state) due to the mechanical restorative force provided by the non-deformable regions of the movable layer 910. When the movable layer 910 is deformed due to actuation, the piezo-electric layer 915 is also deformed and can develop a potential difference across its deformed edges due to the accumulation of charges on the two sides of the piezo-electric layer 915 as discussed above. In some instances, over time the movable layer 910 may not fully return to the un-deformed state due to environmental reasons or due to a reduction in the restorative force provided by the non-deformable regions of the movable layer 910 (for example, caused by material fatigue), and this can result in the movable layer 910 exhibiting effects of stiction. When the movable layer 910 does not fully return to the un-deformed state, the piezo-electric layer 915 may also not return to the un-deformed state. To mitigate or reduce in-use stiction and to return the movable layer 910 to the un-deformed state, the piezo-electric layer 915 may be returned to the un-deformed state by reverse piezo-electric effect. For example, by periodically applying a potential difference across the piezo-electric layer 915, for example, by applying a potential difference between the lead wires 918a and 918b of
Various implementations of the method can include forming a top layer or a metal cap layer on the movable layer prior to forming the piezo-electric layer. In various implementations, the top layer or the metal cap layer can be patterned have a first portion and a second portion, the first and second portions being separated from each other by an opening. The piezo-electric layer is formed such that a portion of the piezo-electric layer extends into the opening. Various implementations of the method can include forming an electrode layer over the piezo-electric layer. The electrode layer and the top layer or the metal cap layer can be formed by depositing an electrical conducting material (for example, metal) over the piezo-electric layer or the movable layer.
The display device 40 includes a housing 41, a display 30, an antenna 43, a speaker 45, an input device 48, and a microphone 46. The housing 41 can be formed from any of a variety of manufacturing processes, including injection molding, and vacuum forming. In addition, the housing 41 may be made from any of a variety of materials, including, but not limited to: plastic, metal, glass, rubber, and ceramic, or a combination thereof. The housing 41 can include removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols.
The display 30 may be any of a variety of displays, including a bi-stable or analog display, as described herein. In various implementations, the display 30 can include a plurality of display elements, each display element including at least one electromechanical systems device having a piezo-electric layer as described above. The display 30 also can be configured to include a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD, or a non-flat-panel display, such as a CRT or other tube device. In addition, the display 30 can include an interferometric modulator display, as described herein.
The components of the display device 40 are schematically illustrated in
The network interface 27 includes the antenna 43 and the transceiver 47 so that the display device 40 can communicate with one or more devices over a network. The network interface 27 also may have some processing capabilities to relieve, e.g., data processing requirements of the processor 21. The antenna 43 can transmit and receive signals. In some implementations, the antenna 43 transmits and receives RF signals according to the IEEE 16.11 standard, including IEEE 16.11(a), (b), or (g), or the IEEE 802.11 standard, including IEEE 802.11a, b, g or n. In some other implementations, the antenna 43 transmits and receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna 43 is designed to receive code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), Global System for Mobile communications (GSM), GSM/General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), Terrestrial Trunked Radio (TETRA), Wideband-CDMA (W-CDMA), Evolution Data Optimized (EV-DO), NEV-DO, EV-DO Rev A, EV-DO Rev B, High Speed Packet Access (HSPA), High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Evolved High Speed Packet Access (HSPA+), Long Term Evolution (LTE), AMPS, or other known signals that are used to communicate within a wireless network, such as a system utilizing 3G or 4G technology. The transceiver 47 can pre-process the signals received from the antenna 43 so that they may be received by and further manipulated by the processor 21. The transceiver 47 also can process signals received from the processor 21 so that they may be transmitted from the display device 40 via the antenna 43.
In some implementations, the transceiver 47 can be replaced by a receiver. In addition, the network interface 27 can be replaced by an image source, which can store or generate image data to be sent to the processor 21. The processor 21 can control the overall operation of the display device 40. The processor 21 receives data, such as compressed image data from the network interface 27 or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor 21 can send the processed data to the driver controller 29 or to the frame buffer 28 for 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.
The processor 21 can include a microcontroller, CPU, or logic unit to control operation of the display device 40. The conditioning hardware 52 may include amplifiers and filters for transmitting signals to the speaker 45, and for receiving signals from the microphone 46. The conditioning hardware 52 may be discrete components within the display device 40, or may be incorporated within the processor 21 or other components.
The driver controller 29 can take the raw image data generated by the processor 21 either directly from the processor 21 or from the frame buffer 28 and can re-format the raw image data appropriately for high speed transmission to the array driver 22. In some implementations, the driver controller 29 can re-format 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 array 30. Then the driver controller 29 sends the formatted information to the array driver 22. Although a driver controller 29, such as an LCD controller, is often associated with the system processor 21 as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. For example, controllers may be embedded in the processor 21 as hardware, embedded in the processor 21 as software, or fully integrated in hardware with the array driver 22.
The array driver 22 can receive the formatted information from the driver controller 29 and can re-format the video data into a parallel set of waveforms that are applied many times per second to the hundreds, and sometimes thousands (or more), of leads coming from the display's x-y matrix of pixels. In various implementations, the array driver 22 can be configured to provide a de-stiction pulse from the voltage source 1140 described above and/or activate the de-stiction switches 1130 described above periodically (for example, in between frames or a few times every hour, or a few times every week) to provide an additional mechanical restorative force to the plurality of display elements.
In some implementations, the driver controller 29, the array driver 22, and the display array 30 are appropriate for any of the types of displays described herein. For example, the driver controller 29 can be a conventional display controller or a bi-stable display controller (e.g., an IMOD controller). Additionally, the array driver 22 can be a conventional driver or a bi-stable display driver (e.g., an IMOD display driver). Moreover, the display array 30 can be a conventional display array or a bi-stable display array (for example, a display including an array of IMODs). In some implementations, the driver controller 29 can be integrated with the array driver 22. Such an implementation is common in highly integrated systems such as cellular phones, watches and other small-area displays.
In some implementations, the input device 48 can be configured to allow, e.g., a user to control the operation of the display device 40. The input device 48 can include a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a rocker, a touch-sensitive screen, or a pressure- or heat-sensitive membrane. The microphone 46 can be configured as an input device for the display device 40. In some implementations, voice commands through the microphone 46 can be used for controlling operations of the display device 40.
The power supply 50 can include a variety of energy storage devices as are well known in the art. For example, the power supply 50 can be a rechargeable battery, such as a nickel-cadmium battery or a lithium-ion battery. The power supply 50 also can be a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell or solar-cell paint. The power supply 50 also can be configured to receive power from a wall outlet.
In some implementations, control programmability resides in the driver controller 29 which can be located in several places in the electronic display system. In some other implementations, control programmability resides in the array driver 22. The above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.
The various illustrative logics, logical blocks, modules, circuits and algorithm steps described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. The interchangeability of hardware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and steps described above. Whether such functionality is implemented in hardware or software depends upon the particular application and design constraints imposed on the overall system.
The hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or, any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular steps and methods may be performed by circuitry that is specific to a given function.
In one or more aspects, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and their structural equivalents thereof, or in any combination thereof. Implementations of the subject matter described in this specification also can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage media for execution by, or to control the operation of, data processing apparatus.
Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations. Additionally, a person having ordinary skill in the art will readily appreciate, the terms “upper” and “lower” are sometimes used for ease of describing the figures, and indicate relative positions corresponding to the orientation of the figure on a properly oriented page, and may not reflect the proper orientation of the IMOD as implemented.
Certain features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.
