Patent Application
20140210836
This disclosure relates to electromechanical systems and devices, and in particular, to systems and methods for improving the reliability and robustness of electromechanical display devices.
Electromechanical systems (EMS) include devices having electrical and mechanical elements, actuators, transducers, sensors, optical components such as mirrors and optical films, and electronics. EMS devices or elements 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 EMS device is called an interferometric modulator (IMOD). The term IMOD 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 IMOD display element 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. For example, one plate may include a stationary layer deposited over, on or supported by 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 IMOD display element. IMOD-based display 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.
Each IMOD display element may be associated with an actuation voltage, which causes the two conductive plates to move toward one another when the actuation voltage is applied across the two plates. The actuation voltage for a particular display element may be based on various factors, including the geometry, structure, and/or materials that form the display element. In particular, each display element can be calibrated to display a particular color when the actuation voltage is applied across the two plates. When a display element becomes uncalibrated, or out-of-tune, unwanted actuations or unwanted releases of the display element may occur, which can introduce undesirable image artifacts into an image to be displayed. Accordingly, it can be important to ensure that display elements remain calibrated under various operating conditions and parameters.
The systems, methods and devices of this 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 display element having an actuated state and a relaxed state. The electromechanical display element can include a fixed optical element having a dielectric layer applied over a transparent or semi-transparent conductive layer, and a movable reflective element having a reflective conductive layer applied over a buffer dielectric layer. A gap can be defined by the dielectric layer and the buffer dielectric layer when the electromechanical display element is in the relaxed state. The buffer dielectric layer can be proximate the dielectric layer when the electromechanical display element is in the actuated state. A thickness of the buffer dielectric layer can be selected such that, in the actuated state, electrons that are photoelectrically ejected from the reflective conductive layer are substantially prevented from being injected into the dielectric layer from the reflective conductive layer.
In some implementations, the buffer dielectric layer can have a thickness in a range of about 50 Å to about 300 Å. Further, the electromechanical display element can be configured to actuate from the relaxed state to the actuated state when an actuation voltage is applied across the transparent or semi-transparent conductive layer and the reflective conductive layer. The thickness of the buffer dielectric layer can be further selected such that the actuation voltage is substantially independent of the thickness of the buffer dielectric layer. In some arrangements, the thickness of the buffer dielectric layer can be selected such that, in the actuated state, electrons in the reflective conductive layer that are excited by photons having energies in a range of about 1.6 eV to about 3.6 eV are substantially prevented from being injected into the dielectric layer from the reflective conductive layer.
Another innovative aspect of the subject matter described in this disclosure can be implemented in a method for manufacturing one or more electromechanical display elements having an actuated state and a relaxed state. The method can comprise applying a transparent or semi-transparent conductive layer on a base layer, and applying a dielectric layer over the transparent or semi-transparent conductive layer. A sacrificial layer can be applied over the dielectric layer, and a buffer dielectric layer can be applied over the sacrificial layer. The method can further include applying a reflective conductive layer over the buffer dielectric layer, and removing the sacrificial material to define a gap between the dielectric layer and the buffer dielectric layer. A thickness of the buffer dielectric layer can be selected such that, upon actuation to move the dielectric layer to be proximate the buffer dielectric layer, electrons that are photoelectrically ejected from the reflective conductive layer are substantially prevented from being injected into the dielectric layer from the reflective conductive layer.
In some implementations, the method can include applying a first dielectric layer under the buffer dielectric layer and applying a second dielectric layer over the dielectric layer. Further, in some implementations, applying the sacrificial layer includes applying amorphous silicon.
Another innovative aspect of the subject matter described in this disclosure can be implemented in a display apparatus. The display apparatus can include a plurality of electromechanical display elements. Each electromechanical display element can have an actuated state and a relaxed state. The electromechanical display element can include a movable reflective element. The electromechanical display element can further include a fixed optical element, wherein a gap can be defined by the movable reflective element and the fixed optical element when the electromechanical display element is in the relaxed state. The movable reflective element can be proximate the fixed optical element when the electromechanical display element is in the actuated state. The movable reflective element can include means for preventing electrons that are photoelectrically ejected from the movable reflective element from being injected into the fixed optical element when the electromechanical display element is in the actuated state.
Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Although the examples provided in this disclosure are primarily described in terms of EMS and MEMS-based displays the concepts provided herein may apply to other types of displays such as liquid crystal displays, organic light-emitting diode (“OLED”) displays, and field emission displays. 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 description is directed to certain implementations for the purposes of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The described implementations may be implemented in any device, apparatus, or system that can be configured to display an image, whether in motion (such as video) or stationary (such as still images), and whether textual, graphical or pictorial. More particularly, it is contemplated that the described implementations may be included 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, global positioning system (GPS) receivers/navigators, cameras, digital media players (such as MP3 players), camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (for example, e-readers), computer monitors, auto displays (including odometer and speedometer displays, etc.), cockpit controls and/or displays, camera view displays (such as the 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 (such as in electromechanical systems (EMS) applications including microelectromechanical systems (MEMS) applications, as well as non-EMS applications), aesthetic structures (such as display of images on a piece of jewelry or clothing) and a variety of EMS 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 one having ordinary skill in the art.
Various implementations disclosed herein can be implemented to reduce image artifacts that are induced when excessive charge is injected into one or more layers of an IMOD display element. IMOD display elements can have an actuated state and an unactuated, or relaxed, state. As explained herein, the two conductive plates or layers of an IMOD display element may be actuated, or brought close to or proximate one another, when an actuation voltage is applied across the two conductive layers. Similarly, the display element may be unactuated, or relaxed, when a sufficiently low release voltage is applied across the conductive layers. When the display element is in the relaxed state, a gap is defined between the two conductive plates. When sunlight impinges on an IMOD display device, photons may be absorbed by one or more of the IMOD's layers for display elements in the actuated state. The absorbed photons may excite electrons within one or more of the conductive layer(s), and the excited electrons may be photoelectrically ejected from the conductive layer(s) of the display element, (for example, in a movable reflective layer) to a dielectric layer in the other layer of the display element (e.g., a stationary or fixed optical stack). The electrons injected into the other layer, such as a dielectric layer in the optical stack, may cause charge to build up in the optical stack. The charge build-up in the optical stack can cause a negative offset voltage shift, which can cause the actuation and/or release voltage for the display element to change. Thus, when the previously-calibrated actuation (or release) voltage is applied across the two conductive layers, the display element may not properly actuate (or release). Further, in some arrangements, the negative offset voltage shift can cause unintended actuation and/or unintended release. In general, therefore, the negative offset voltage shift caused by charge build-up in the optical stack can cause IMOD display elements to become uncalibrated and/or “out-of-tune” in some cases. The uncalibrated and out-of-tune display elements can cause undesirable image artifacts, such as stripes and/or dark regions in portions of the display. Accordingly, it can be desirable to reduce the image artifacts caused by charge injection into the optical stack.
In various implementations disclosed herein, a buffer layer can be applied to the movable reflective layer that can act to block charges from being ejected from the movable reflective layer into the optical stack. For example, a first dielectric layer can be applied over a first conductive layer of the optical stack. A movable reflective layer that is configured to actuate by moving proximate the movable stack can include a second conductive layer that is applied over a second dielectric layer (for example, the buffer layer) of the movable reflective layer. Thus, in some implementations, when the display element is in the actuated state, the first dielectric layer of the optical stack may be proximate the second dielectric layer (for example, the buffer layer) of the movable reflective layer. The second dielectric layer of the movable reflective layer may have a thickness that is selected such that, when the display element is in the actuated state, electrons that are photoelectrically ejected from the second conductive layer of the movable reflective layer are substantially prevented from being injected into the first dielectric layer of the optical stack. By substantially preventing such charge injection or migration, negative offset voltage shifts and undesirable image artifacts can be reduced. Those skilled in the art will appreciate that it is not necessary for the second dielectric layer to block injection of all photoelectrically ejected electrons in order to attain desirable improvements in image quality.
Thus, those skilled in the art will understand that determining whether a particular thickness of a buffer layer provides substantial prevention of injection of photoelectrically ejected electrons can be evaluated in various ways and/or using various metrics. As one example, the display elements can be physically examined using various microscopy techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), etc. For example, these imaging techniques can be used to determine the type of material used in the buffer layer and/or the thickness of the buffer layer. In other examples, usage tests may be conducted to qualitatively determine how image artifacts arise over time when the display device is exposed to direct lighting conditions. In yet other examples, determining whether a particular thickness of a buffer layer provides substantial prevention of injection of photoelectrically ejected electrons can be evaluated by measuring offset voltage shifts. For example, in one implementation, if the offset voltage for a particular display element changes by less than or equal to a particular threshold amount after being exposed to light for a predetermined period of time, then it can be determined that the buffer layer is suitably thick to prevent charge injection. For example, in some arrangements, the predetermined period of exposure time can be in a range of about 100 hours to about 500 hours. In other arrangements, however, the predetermined period of exposure time can be less, such as about a day or two. For example, if the offset voltage shifts by less than or equal to about 1 volt over the predetermined time period, then it can be determined that the buffer layer is sufficiently thick. In another example, if the offset voltage shifts by less than or equal to about 0.6 volts over the predetermined time period, or alternatively by less than or equal to about 0.3 volts over the predetermined time period, then it can be determined that the buffer layer is sufficiently thick.
In other implementations, if the measured offset voltage for a particular display element is within a precalibrated voltage range after being exposed to sunlight for a particular period of time, then it can be determined that the buffer layer has a sufficient thickness to substantially prevent the injection of photoelectrically injected electrons. As explained herein with respect to
Thus, in various implementations disclosed herein, the thickness of the buffer layer can be selected to block charges from migrating from the movable reflective layer to the optical stack. In particular, the thickness of the buffer layer may be selected such that electrons in the second conductive layer of the movable reflective layer that are excited by photons within a particular energy range are substantially prevented from being injected into the optical stack. For example, the thickness of the buffer layer may be selected to block electrons excited by photons having energies in a range of about 1.6 eV to about 3.6 eV. In some arrangements, the thickness of the buffer layer may be in a range of about 50 Å to about 300 Å. For example, the thickness of the buffer layer may be in a range of about 80 Å to about 200 Å. Further, the thickness of the buffer layer may be in a range of about 90 Å to about 120 Å. The buffer layer can include any suitable dielectric material, such as, for example, silicon dioxide.
The thickness of the buffer layer can be further selected such that the actuation voltage (and/or the release voltage) is substantially independent of the thickness of the buffer layer. If the buffer layer is made to be too thick, for example, then the actuation voltage for the display element may increase, which may disrupt the driving scheme for the display. Thus, in some implementations, the thickness of the buffer layer is selected such that the buffer layer thickness remains in a regime where its thickness does not substantially affect the actuation and/or release voltages of the display element compared to the actuation and/or release voltages without the presence of the buffer layer.
In some implementations disclosed herein, a sacrificial material that is used to define an air gap of the display element may also be selected to reduce manufacturing costs and/or to improve device yield. For example, as explained in more detail herein, Molybdenum (Mo) is often used as a sacrificial material. Skilled artisans will appreciate that Mo is relatively expensive to apply using various processes. Furthermore, Mo may not be applied with a uniform thickness in some instances, which can cause a loss of device yield because the resulting air gap may have a varying height across the display element. As disclosed herein, amorphous silicon (α-Si) may instead be used as the sacrificial layer. In some implementations, for example, the α-Si sacrificial layer may be applied directly over a silicon dioxide (SiO2) layer. Applying α-Si over a SiO2 layer instead of over an aluminum oxide (Al2O3) layer may improve the adhesion of the sacrificial layer to the optical stack. Skilled artisans will appreciate that α-Si may be relatively inexpensive and can be applied to uniform thicknesses. Thus, by using α-Si as the sacrificial layer in some implementations disclosed herein, processing costs may be reduced and/or device yield may be increased.
Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. As explained herein, exposure to sunlight may cause charge injection into the optical stack. Adding a buffer layer to the movable reflective layer can prevent electrons from being ejected out of the movable reflective layer and into the optical stack when the display element is in the actuated state. Preventing such charge injection into the optical stack can reduce image artifacts associated with a negative offset voltage drift.
Implementations disclosed herein may also offer one or more processing improvements. For example, in some arrangements, applying the additional buffer layer to the movable reflective layer may reduce damage that can occur to the display element during processing. The buffer layer can prevent metal (for example, aluminum) from migrating from the movable reflective layer to an amorphous silicon sacrificial layer during high temperature processing. Such material migration can create particles and pits in portions of the display element. Furthermore, the use of the buffer layer can enable the use of amorphous silicon as the sacrificial layer instead of Molybdenum in some implementations, thereby reducing processing costs, and/or improving device yield.
An example of a suitable EMS or MEMS device or apparatus, to which the described implementations may apply, is a reflective display device. Reflective display devices can incorporate interferometric modulator (IMOD) display elements that can be implemented to selectively absorb and/or reflect light incident thereon using principles of optical interference. IMOD display elements can include a partial optical absorber, a reflector that is movable with respect to the absorber, and an optical resonant cavity defined between the absorber and the reflector. In some implementations, 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 IMOD. The reflectance spectra of IMOD display elements can create fairly broad spectral bands that 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. One way of changing the optical resonant cavity is by changing the position of the reflector with respect to the absorber.
The IMOD display device can include an array of IMOD display elements which may be arranged in rows and columns. Each display element in the array can include at least a pair of reflective and semi-reflective layers, such as a movable reflective layer (i.e., a movable layer, also referred to as a mechanical layer) and a fixed partially reflective layer (i.e., a stationary layer), positioned at a variable and controllable distance from each other to form an air gap (also referred to as an optical gap, cavity or optical resonant cavity). The movable reflective layer may be moved between at least two positions. For example, in a first position, i.e., a relaxed position, the movable reflective layer can be positioned at a 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 and/or destructively depending on the position of the movable reflective layer and the wavelength(s) of the incident light, producing either an overall reflective or non-reflective state for each display element. In some implementations, the display element may be in a reflective state when unactuated, reflecting light within the visible spectrum, and may be in a dark state when actuated, absorbing and/or destructively interfering light within the visible range. In some other implementations, however, an IMOD display element 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 display elements to change states. In some other implementations, an applied charge can drive the display elements to change states.
The depicted portion of the 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 and/or molybdenum), 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, certain portions of the optical stack 16 can include a single semi-transparent thickness of metal or semiconductor which serves as both a partial optical absorber and electrical conductor, while different, electrically more conductive layers or portions (e.g., of the optical stack 16 or of other structures of the display element) can serve to bus signals between IMOD display elements. The optical stack 16 also can include one or more insulating or dielectric layers covering one or more conductive layers or an electrically conductive/partially absorptive layer.
In some implementations, at least some of 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 ordinary 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 supports, such as the illustrated posts 18, and an intervening sacrificial material located 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 μm, while the gap 19 may be approximately less than 10,000 Angstroms (Å).
In some implementations, each IMOD display element, whether in the actuated or relaxed state, can be considered as 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 display element 12 on the left in
The details of the structure of IMOD displays and display elements may vary widely.
As illustrated in
In implementations such as those shown in
In
The process 80 continues at block 84 with the formation of a sacrificial layer 25 over the optical stack 16. Because the sacrificial layer 25 is later removed (see block 90) to form the cavity 19, the sacrificial layer 25 is not shown in the resulting IMOD display elements.
The process 80 continues at block 86 with the formation of a support structure such as a support post 18. The formation of the support post 18 may include patterning the sacrificial layer 25 to form a support structure aperture, then depositing a material (such as a polymer or an inorganic material, like silicon oxide) into the aperture to form the support post 18, using a deposition method such as PVD, PECVD, thermal CVD, or spin-coating. In some implementations, the support structure aperture formed in the sacrificial layer can extend through both the sacrificial layer 25 and the optical stack 16 to the underlying substrate 20, so that the lower end of the support post 18 contacts the substrate 20. Alternatively, as depicted 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 19. The cavity 19 may be formed by exposing the sacrificial material 25 (deposited at block 84) to an etchant. For example, an etchable sacrificial material such as Mo or amorphous Si may be removed by dry chemical etching by exposing the sacrificial layer 25 to a gaseous or vaporous etchant, such as vapors derived from solid XeF2 for a period of time that is effective to remove the desired amount of material. Various implementations disclosed herein may also utilize a buffer layer (for example, silicon dioxide) that can prevent metal migration (such as aluminum) from the movable reflective layer to an amorphous-Si sacrificial layer. The sacrificial material is typically selectively removed relative to the structures surrounding the cavity 19. Other etching methods, such as wet etching and/or plasma etching, also may be used. Since the sacrificial layer 25 is removed during block 90, the movable reflective layer 14 is typically movable after this stage. After removal of the sacrificial material 25, the resulting fully or partially fabricated IMOD display element may be referred to herein as a “released” IMOD.
The optical stack 116 may be applied over a transparent substrate 120, similar to the substrate 20 described herein. The optical stack 116 may be similar to the optical stack 16 described above with respect to FIGS. 1 and 2A-2E, except the optical stack 116 shown in
Unlike the implementation of
Further, a first dielectric sub-layer 116b may be applied over the optical absorber layer 116a, and a second dielectric sub-layer 116c may be applied over the first dielectric sub-layer 116b, as shown in
The sacrificial layer 125 may be applied over the second dielectric sub-layer 116c. In various arrangements, the sacrificial layer 125 is molybdenum (Mo) or amorphous silicon, although other sacrificial materials may be used. As explained herein, when the sacrificial layer 125 is selectively removed, an air gap is formed between the optical stack 116 and the movable reflective layer 114. Further, as explained above, Al2O3 can be used in the optical stack 116 as the second dielectric sub-layer 116c. The Al2O3 sub-layer 116c may act as an etch stop when Mo is used as the sacrificial material 125.
The movable reflective layer 114 can include a reflective layer 114a, a support layer 114b, and a conductive layer 114c, which may be configured to serve as an electrode. As shown in
In some implementations, when the display element 112 is actuated, the second dielectric sub-layer 116c may stick to the reflective layer 114a when a release voltage is subsequently applied. Such stiction may affect the display quality of the IMOD display. To reduce stiction, a first interface dielectric 111a may be applied over the outer or bottom surface of the reflective layer 114a of the movable reflective layer 114. Similarly, a second interface dielectric 111b may be applied over the outer or top surface of the second dielectric sub-layer 116c of the optical stack 116. Thus, as shown in
The first and second interface dielectrics 111a and 111b may be formed to be very thin in some arrangements so as not to affect the actuation and/or release voltages of the display element 112. In some implementations, the first and second interface dielectrics 111a and 111b may be applied after the display element 112 is released, for example, after selectively removing the sacrificial material 125. For example, apertures in the display element 112 may be provided that allow an atomic layer deposition (ALD) process to be performed. In some implementations, therefore, an ALD process may be used after release to deposit aluminum oxide as the first and second interface dielectrics 111a and 111b. For example, in some arrangements, each of the first and second interface dielectrics may independently have a thickness in a range of about 10 Å to about 500 Å. More particularly, each of the first and second interface dielectrics may independently have a thickness in a range of about 20 Å to about 150 Å. Other suitable dielectrics may be used to prevent stiction. Furthermore, while the interface dielectrics 111a and 111b are described as being deposited using ALD, it should be appreciated that any other suitable method may be used, including methods that apply the interface dielectrics 111a and 111b before the sacrificial material 125 is removed.
As explained above, when an IMOD display is used in bright lighting conditions, such as under direct sunlight, photons can pass through the optical stack 116 and can impinge on the movable reflective layer 114. For example, as shown in
In some arrangements, a filter (not illustrated in
The charge that is trapped within the optical stack 116 (e.g., at interfaces in the stack 116, within the first and second dielectric sub-layers 116c and 116d, etc.) may induce a negative offset voltage shift. As explained above, this negative offset voltage shift may induce image artifacts when display elements are unintentionally actuated or released, or when the applied voltage (whether for actuation, hold, or release), does not properly actuate, hold, or release the display element. As explained herein, one way to mitigate the image artifacts that are induced when charge is injected into the optical stack 116 is to apply a buffer layer between the reflective layer 114a and the sacrificial layer 125 shown in
By contrast, when the buffer layer is included in the movable reflective layer 114 between the reflective layer 114a and the sacrificial layer 125 (see, for example, the buffer layer 214d between the reflective layer 214a and the sacrificial layer 225 of
The optical stack 216 of
Unlike the implementation of
As shown in
As explained above with respect to
The buffer layer 214d may be sufficiently thick so as to block the excited electrons 209 from being injected into the optical stack 216. However, the thickness of the buffer layer 214d may be limited by the actuation and/or release voltages designed for a particular drive scheme. For example, it may be undesirable to use a buffer layer 214d that has a very large thickness. While a very large thickness may block electrons from being injected into the optical stack 216, an excessively thick buffer layer 214d may accordingly increase the actuation voltage to unacceptable levels for the driving scheme. Thus, the thickness of the buffer layer 214d may be selected to be thick enough to block electrons from being injected into the optical stack, yet thin enough such that the actuation voltage remains substantially unaffected. Thus, the thickness of the buffer layer 214d may be selected such that the thickness of the buffer layer 214d remains in a regime such that the actuation voltage (and/or release voltage) is substantially independent of changes in the thickness of the buffer layer 214d.
In some implementations, the thickness of the buffer layer 214d may be selected such that, in the actuated state, electrons 209 in the reflective layer 214a that are excited by photons 208 having energies in a range of about 1.6 eV to about 3.6 eV are substantially prevented from being injected into the optical stack 216, for example, into the first and/or second dielectric sub-layers 216b and/or 216c. For example, as explained above, the energy barrier height for the interface between the reflective layer 114a and the first and second interface dielectrics 111a and 111b without a buffer layer can be about 2.1 eV. When the buffer layer 214d is present below the reflective layer 214a as illustrated in
In the implementation of
In the implementation of
However, unlike
As with
The method 90 then proceeds to a block 92 to apply a dielectric layer over the transparent conductive layer. In various arrangements, at least one of a PVD and a PECVD process are performed to apply the dielectric layer. The dielectric layer can include one or more sub-layers, or the dielectric layer can be formed of a single material. For example, as explained herein with respect to
Turning to a block 93, a sacrificial material is applied over the dielectric layer. The sacrificial material may be applied and later removed (for example, at block 96) to form the air gap. The sacrificial material may be any suitable sacrificial material, such as molybdenum or amorphous silicon. When molybdenum is used as the sacrificial material, in some implementations, the molybdenum sacrificial material may be applied over an aluminum oxide layer. In other implementations, when amorphous silicon is used as the sacrificial material, the amorphous silicon sacrificial material may be applied over a silicon dioxide layer for improved adhesion.
The method 90 moves to a block 94 to apply a buffer dielectric layer over the sacrificial layer. The buffer dielectric layer can act as a buffer layer as described herein to prevent electrons from being photoelectrically ejected from the movable reflective layer to the optical stack. In some implementations, the buffer dielectric layer can include silicon dioxide, however, other dielectric materials may be suitable. The buffer dielectric layer may be applied by performing a PVD process and/or a PECVD process.
Turning to a block 95, a reflective conductive layer is applied over the buffer dielectric layer. In some implementations, the reflective conductive layer may act as the reflective layer of the movable reflective layer described herein. For example, the reflective conductive layer may include aluminum or aluminum-copper. In some implementations, the reflective conductive layer is not fully reflective, and may only be semi-reflective.
The method 90 moves to a block 96 to remove the sacrificial material to release the display element. As explained herein, an etching process (e.g., a wet etch, dry etch, plasma etch, etc.) may be performed to remove the sacrificial material. For example, Mo and α-Si sacrificial materials may be removed using an XeF2 etch process. Skilled artisans will understand that various combinations of etchants and sacrificial materials may be suitable.
In some implementations, a first atomic deposition layer may be applied under the buffer dielectric layer, and a second atomic deposition layer may be applied over the dielectric layer. For example, the first and second atomic deposition layers may correspond to the first and second interface dielectrics described herein. In some implementations, the first and second atomic deposition layers may be applied after removing the sacrificial material. For example, an ALD process may be used to apply the first and second atomic deposition layers. In some implementations, the first and second atomic deposition layers may include aluminum oxide. Further, as explained herein, the buffer dielectric layer of the movable reflective layer may have a thickness that is selected such that, when the display element is in the actuated state, electrons that are photoelectrically ejected from the reflective conductive layer of the movable reflective layer are substantially prevented from being injected into the dielectric layer of the optical stack. It should be appreciated that, as disclosed herein, other intervening layers may be applied in some implementations. The first and second atomic deposition layers may be used to reduce stiction. Although the first and second atomic deposition layers are disclosed herein as being formed using an ALD process in some implementations, it should be appreciated that other processes may be used to form the first and second atomic deposition layers. For example, other types of processes may be used to create thin dielectric layers (such as the first and second interface dielectric layers described above) to prevent or reduce stiction.
Although the steps of the method 90 of
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. 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 IMOD-based display, as described herein. For example, the display 30 can include a plurality of electromechanical display elements (for example, IMODs) that include a fixed optical element having a dielectric layer applied over a transparent or semi-transparent conductive layer. Each display element of the plurality of display elements can include a movable reflective element having a reflective conductive layer applied over a buffer dielectric layer. A gap can be defined by the dielectric layer and the buffer dielectric layer when the electromechanical display element is in the relaxed state, and the dielectric layer can be proximate the buffer dielectric layer when the electromechanical display element is in the actuated state. A thickness of the buffer dielectric layer can be selected such that, in the actuated state, electrons that are photoelectrically ejected from the reflective conductive layer are substantially prevented from being injected into the dielectric layer from the reflective conductive layer.
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, for example, 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, n, and further implementations thereof. 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 can be 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, 4G or 5G 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, in some implementations, 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 can be 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 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 (such as an IMOD display element controller). Additionally, the array driver 22 can be a conventional driver or a bi-stable display driver (such as an IMOD display element driver). Moreover, the display array 30 can be a conventional display array or a bi-stable display array (such as a display including an array of IMOD display elements). In some implementations, the driver controller 29 can be integrated with the array driver 22. Such an implementation can be useful in highly integrated systems, for example, mobile phones, portable-electronic devices, watches or small-area displays.
In some implementations, the input device 48 can be configured to allow, for example, 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, a touch-sensitive screen integrated with the display array 30, 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. For example, the power supply 50 can be a rechargeable battery, such as a nickel-cadmium battery or a lithium-ion battery. In implementations using a rechargeable battery, the rechargeable battery may be chargeable using power coming from, for example, a wall socket or a photovoltaic device or array. Alternatively, the rechargeable battery can be wirelessly chargeable. 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.
As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.
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 also may be implemented as a combination of computing devices, such as 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.
If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. The steps of a method or algorithm disclosed herein may be implemented in a processor-executable software module which may reside on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program from one place to another. A storage media may be any available media that may be accessed by a computer. By way of example, and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Also, any connection can be properly termed a computer-readable medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above also may be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and instructions on a machine readable medium and computer-readable medium, which may be incorporated into a computer program product.
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. 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, for example, an IMOD display element 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, a person having ordinary skill in the art will readily recognize that such operations need not 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.
