Microelectromechanical system contactor spring

Abstract

Embodiments of the present application relate to a microelectromechanical system contactor spring. In described examples, a system (e.g., a microelectromechanical system (200)) includes a substrate (208), a support (210) coupled to the substrate (208), and a first element (203) and a second element (201). The first element (203) includes a contactor spring (204) having a first portion coupled to the support and having a second portion including a cavity having a sloped surface. A clearance from the sloped surface to the substrate (208) widens as the sloped surface extends away from the first portion. The second portion includes a first contact surface adjacent the sloped surface. The second element (201) is coupled to the substrate and has a second contact surface adjacent the first contact surface. One of the first element (203) and the second element (201) is adapted to: urge the first contact surface and the second contact surface together in a first direction; and urge the first contact surface and the second contact surface apart in a second direction.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to a microelectromechanical system contactor spring. BACKGROUND

[0002] Microelectromechanical systems (MEMS) can include devices such as actuators, switches, motors, sensors, variable capacitors, and spatial light modulators (SLMs). MEMS devices can be fabricated on a substrate. To protect such devices, sidewalls are formed on the substrate during fabrication to form a sealable cavity, such that the structures and devices within the cavity can be relatively isolated from the outside environment. However, contaminants can gradually migrate into the cavity and can react with or otherwise interfere with the proper operation of the devices contained within the cavity. SUMMARY

[0003] In described examples, a system (e.g., a microelectromechanical system) includes a substrate, a support coupled to the substrate, and a first element and a second element. The first element includes a contactor spring having a first portion coupled to the support and having a second portion including a cavity having a tilted surface. A clearance from the tilted surface to the substrate widens as the tilted surface extends away from the first portion. The second portion includes a first contact surface adjacent the tilted surface. The second element is coupled to the substrate and has a second contact surface adjacent the first contact surface. One of the first element and the second element is adapted to: urge the first contact surface and the second contact surface together in a first direction; and urge the first contact surface and the second contact surface apart in a second direction. BRIEF DESCRIPTION OF DRAWINGS

[0004] Figure 1 A representative component of an example image display system is shown.

[0005] Figure 2 is Figure 1 An exploded view of an example structure of a pixel modulator element of an image display system.

[0006] Figure 3 A cross-section taken along a diagonal hinge axis of an example pixel element is shown.

[0007] Figure 4 and Figure 5 are, respectively, a front projection view and an elevation view of an example pixel structure of Figure 2

[0008] Figure 6A , Figure 6B and Figure 6C Example capillary condensation on an example pixel modulator element is shown.​

[0009] Figure 7 is Figure 2 a perspective top view of an example pixel modulator element.

[0010] Figures 8A to 8K is a cross-sectional view showing formation of an example reduced contact surface of an example spring tip.

[0011] Figure 9 shows an example reduced contact surface of an example spring tip. DETAILED DESCRIPTION

[0012] In the drawings, like reference numerals refer to like elements, and various features not necessarily drawn to scale.

[0013] Microelectromechanical systems (MEMS) devices, such as actuators, switches, motors, sensors, variable capacitors, and spatial light modulators, can have movable elements. For example, a spatial light modulator (SLM) device can include an array of movable elements, such as pixel modulator elements. Each such element can be an individually addressable light modulator element, where a "on" or "off position is set in response to input data. The input data can be image information, which is used to program the individual light modulator elements of the array to project light directed from an illumination source toward the array or to turn the light aside.

[0014] In an example SLM device of an image projection system, the input data includes bit frames generated in response to pixel chrominance and intensity information data of image frames of an image input signal. The bit frames can be projected using a pulse width modulation scheme. The pulse width modulation scheme includes weighted time intervals for projecting pixels of the pixel chrominance and intensities corresponding to respective pixels in the input data. The weighted time intervals are long enough to allow human eye integration within a given image frame display period. An example of the SLM device is a digital micromirror device (DMD), such as Texas Instruments DMD® micromirror two-dimensional array device. Such DMD devices have been used commercially in a wide variety of devices, such as televisions, movie projection systems, business-related video projectors, and micro projectors.

[0015] A DMD device can be manufactured to include micromirrors to digitally image and project a digital image onto a display surface, such as a projection screen. For example, a projector system can include a DMD device arranged to modulate an incident light beam received through a window glass of the DMD device and focused on micromirrors therein. Selected micromirrors can be individually and dynamically adjusted in response to input data to project a selected visual image onto a projection screen.

[0016] Individual micromirrors may be coupled to (e.g., mounted on and / or supported by) a torsion spring. The torsion spring may be arranged as a hinge containing an axis (e.g., a longitudinal axis) about which the micromirror can rotate. In a configuration where the micromirror is "hard over," the micromirror contacts (e.g., impacts) a landing surface. Contact with the micromirror may encounter environmentally induced adhesive (e.g., sticking) forces that prevent the micromirror from bouncing off the landing surface. This sticking may originate from environmental contamination (e.g., moisture) and can lead to improper operation and other reliability problems.

[0017] Figure 1 Representative components of an example image display system are shown. Display system 100 includes a MEMS spatial light modulator (SLM) integrated circuit (IC) arranged to project an image as a spatially modulated projection beam. Light from light source 101 can be directed onto an array of pixel modulator elements 111 and 112, wherein the position of the micromirrors of pixel modulator elements 111 and 112 is individually modulated in synchronization with input image data. Light from light source 101 is directed through projection lens 102 onto the display surface (in a configuration where the elements are in an "on" position) or directed away from the display surface (e.g., to light absorber 103 in a configuration where the elements are in an "off" position). Figure 1 For example, to simply illustrate an array with two modulator elements, a high-resolution array of an IC may contain thousands (or more) of such elements arranged in rows and columns, with each individual element corresponding to a pixel position in a projected image.

[0018] In one example, each pixel modulator element includes a positionable (e.g., rotatably oriented and / or movable) element, such as a micromirror (e.g., 111 or 112), adapted to tilt (e.g., rotate) between two positions (e.g., where the two positions may define opposite directions). This can be achieved via a torsion spring (e.g., described below). Figure 2 203) and support components (e.g., Figure 2 The support member 210 couples the micromirror to the substrate 110. The micromirror includes a micromirror contact surface adjacent to the spring tip (e.g., Figure 2 The surface of the micromirror (e.g., the micromirror surface). The micromirror can abut against the landing element (e.g., as described below regarding...). Figure 5 The described spring tip 204 has a contact surface 501. In a first direction, an electrostatic force can be selectively applied to push the first contact surface and the second contact surface together (e.g., force, pull, position, orient, move, and / or apply force to attempt to move). In a second direction, an electrostatic force can be selectively applied to push the first contact surface and the second contact surface apart.

[0019] As described below, the micromirrors can "stick" to the fixed landing elements in response to a sticking force. For example, the sticking force can be caused by van der Waals force interactions in combination with meniscus / capillary formation operations. Van der Waals forces are affected by the electrical interactions between two or more neighboring atoms or molecules. Capillary tubes (e.g., surface tension induced water molecule aggregation) can form in non-ultra-high vacuum (non-UHV) and non-enclosed systems. Such capillary tubes can be dominated by water and other condensable / mobile species in the top space and around the cavity surfaces used to protect the SLM device.

[0020] The amount of adhesion or sticking between the movable elements and the fixed elements is, for example, a factor of how much force is applied to cause the movable elements to move (e.g., from a neutral position) or release (e.g., from a landing surface). Example structures involving sticking can include contact surfaces (e.g., of movable micromirrors in an SLM) that can be formed as protrusions to reduce the contact surface area, which can reduce the amount of sticking between the micromirror elements and the landing elements. Example SLM devices are described herein, and the accompanying descriptions and methods described herein can be applied to a variety of MEMS components and configurations (e.g., such that the force applied to overcome sticking to help initiate movement of the microelectromechanical structures can be reduced).

[0021] Examples of reduced contact surfaces (e.g., for reducing sticking) are described in commonly-assigned U.S. Patent Application Publication No. US 2018 / 0290880, entitled Isolated Protrusion / Recession Features in a Micro Electro Mechanical System, published October 11, 2018, the entire contents of which are incorporated herein by reference.

[0022] Figure 2 is an exploded view of an example structure of a pixel modulator element of an image display system of Figure 1 The micromirror array arranged on a single integrated circuit (IC) can form an SLM of Figure 1 The optically active portion of an imaging element of an SLM of

[0023] In configurations in which a DMD is coupled to an illumination source and an alignment optical system assembly, the DMD can modulate the amplitude and / or direction of incoming light to create a two-dimensional optical image (picture) or other light pattern. The DMD can be used to modulate light so that a video image can be projected onto a display surface (e.g., a screen). Other uses of the DMD include structured illumination, augmented reality, microscopy, medical instruments, spectroscopy, machine vision, industrial inspection, three-dimensional (3D) scanning, 3D optical metrology, automatic fingerprint recognition, facial recognition, interactive displays, information overlay, chemical analyzers, light stimulation, virtual gauges, and other optical-related applications. The DMD can be used in systems that provide image projection, systems that provide image capture, and systems that include both image projection and image capture. Light sources that can be modulated by the DMD include xenon lamps, laser light sources, LEDs, and excited phosphors.

[0024] CMOS (complementary metal-oxide-semiconductor) technology is employed in processes of fabricating CMOS memory devices. A DMD chip can be fabricated using a CMOS (or similar CMOS) process to fabricate a substrate that includes CMOS memory. The DMD chip includes an array of individually addressable micromirror elements, with selected instances of the micromirrors adapted (e.g., tilted) to reflect light in response to a memory state of a memory cell formed in a substrate (e.g., an underlying substrate).

[0025] A memory cell that can be formed in a substrate can be arranged to include one memory cell within an array of memory cells (e.g., such that the substrate includes an array of memory cells). The memory cell is coupled to an electrostatic electrode, each of which is adapted to selectively move a respective mirror, such that the respective mirror is adapted to reflect light in response to a memory state of the respective memory cell.

[0026] Selected instances of the micromirrors are adapted to reflect light in one of at least two different directions in response to a memory state of a corresponding underlying memory cell. (In some descriptions herein, terms such as “down” and “below” can be used to describe opposite directions that generally extend away from the micromirror and toward the substrate, while terms such as “up” and “above” can be used to describe opposite directions that extend away from the substrate and toward the micromirror.) By combining the DMD chip with an alignment light source and projection optics, the micromirrors can be oriented (e.g., rotated) to reflect incident light to or away from a pupil of a projection lens of the projection optics.

[0027] In examples, a first state of the micromirror corresponds to a bright pixel, and a second state of the micromirror corresponds to a dark pixel. Grayscale of a pixel can be achieved by pulse width modulation (e.g., binary PWM) of incident light (e.g., where the incident light is projected on a display screen). Coloring of a pixel can be achieved by selectively activating light sources of different colors and / or filtering illumination beams using one or more color filters (which can be stationary or rotating) to produce selectively colored projected beams. Selectively colored projected beams can be imaged by coupling one, two, or three or more DMD chips in an optical path configured to produce selectively colored projected beams.

[0028] An example DMD chip can have a variety of architectures, such as an example design including a structure with micromirrors 201 rigidly connected (e.g., by connector supports 211, where the rigid connections are illustrated in a disassembled view of the pixel modulator element 200) to an underlying yoke. The yoke is supported (e.g., connected) by two flexible (e.g., mechanically deflected) torsional springs 203 arms, where the arms are coupled to respective support posts, which in turn are coupled to an underlying substrate (e.g., supported by the underlying substrate). A controlled electrostatic field is generated in a relative region between an underlying memory cell and a respective micromirror, which can cause the supported micromirror to rotate in a selected one of a positive rotational direction and a negative rotational direction.

[0029] Examples of chip fabrication of DMD superstructures described herein include underlying CMOS memory circuitry on which a DMD superstructure is formed. A DMD superstructure can be formed by sequentially forming a series of patterned photoresist layers deposited over an exposed surface of an integrated circuit (e.g., underlying CMOS memory circuitry). Various elements of an example DMD superstructure can be formed in response to a process sequence for stepwise formation of metal layers. For example, an aluminum layer (e.g., for forming address electrodes, hinges, yokes, and micromirrors) can be deposited over a surface of a hardened photoresist (e.g., a photoresist layer of photoresist) and selectively etched to form spatial openings (e.g., voids and / or air gaps) between various superstructure elements in response to a chemical process during which the photoresist layer is removed.

[0030] General operation and construction of a DMD chip is described in U.S. Patent No. 9,348,136, issued May 24, 2016, entitled Micromirror Apparatus and Methods, the entirety of which is incorporated herein by reference. Other examples of MEMS devices employing micromirrors are described in U.S. Patent Nos. 7,011,415 and 7,404,909, the entirety of both of which are incorporated herein by reference.

[0031] A DMD chip can include a micromirror array, a memory array, a data controller receiver, and micromirror array reset control. An example micromirror array can include thousands (or more than a million) of reflective, individually positionable (e.g., individually movable and / or orientable), digitally switchable, micron-sized micromirrors. The micromirror array can be organized into a two-dimensional (e.g., “n” columns by “m” rows) array (or other systematically arranged array).

[0032] The micromirrors can be aluminum elements 1-20 microns in size (e.g., arranged along a 7.6 micron pitch), with at least some of the micromirrors switchable between discrete angular positions. For example, for an “on” state, a selected micromirror can be switched (e.g., tilted) to an angle of +12 degrees, and for an “off’ state, it can be switched to an angle of -12 degrees. The switching angles can be relative to a 0 degree flat reference state (e.g., a “parked” or neutral state). The micromirrors park in an inactive state, with the parked micromirrors parallel to the plane of the array substrate. The parked position in this example generally does not correspond to a latched position (e.g., a position controlled by the on or off state of an underlying memory cell).

[0033] In an ideal example, the surface of the micromirror is flat when rotated between discrete angular positions. The rotation of the micromirror through angular positions can include a tilt angle (e.g., a tilted position), with the tilt angle ideally lying in a conceptual plane that is orthogonal to the hinge axis (e.g., the longitudinal axis of the torsional spring 203). The on state position can include a rotated tilt angle toward one side of the encapsulation package (e.g., the package encapsulating the micromirror), while the off state position can include a rotated tilt angle toward the opposite side of the encapsulation package.

[0034] The memory array can be arranged as a two-dimensional array of 1-bit CMOS memory cells. The memory array can be addressed column-by-column over a double data rate (DDR) bus. The DMD can be controlled in response to control signals asserted by a digital controller chip. The control signals can coordinate storage and latching of information for indicating angular positions of micromirrors of selected pixel modulator elements in an array of pixel modulator elements. At least one of the selected pixel modulator elements in the array of pixel modulator elements includes a respective electrode for electrostatically positioning a respective micromirror in response to a respective memory cell. Each of the individual micromirrors can be arranged adjacent to (e.g., above) a corresponding CMOS memory cell.

[0035] A specific micromirror is adapted to adopt a selected angular position in response to the binary state (e.g., logic 0 or 1) of the corresponding CMOS memory cell (e.g., synchronized with the micromirror clock pulse). Changes in the angular position of an individual micromirror (e.g., +12 degrees or -12 degrees) may be synchronized with the micromirror clock pulse, but this is not necessarily consistent with memory cell data updates. In an example, writing a logic 1 state to a memory cell before the micromirror clock pulse causes the corresponding micromirror to switch to the +12 degree on position, and writing a logic 0 state to a memory cell before the micromirror clock pulse causes the corresponding micromirror to switch to the -12 degree off position.

[0036] The angular position of the micromirror array can be updated through two operations. In the first operation, the contents of the memory are updated by addressing and latching a selected value in the addressed memory cell. In the second operation, a micromirror reset signal can be applied to the entire (or other) portion of the micromirror array (e.g., depending on the associated system architecture). The micromirror reset pulse can be generated internally by the DMD chip, and the application of the micromirror reset pulse is coordinated by a digital controller.

[0037] Pixel modulator element 200 includes a micromirror 201 coupled (e.g., supported by) a support post 202 to a torsion spring 203 (e.g., arranged as a torsion hinge). In response to a change in the angular position of a selected micromirror, a portion of the lower surface of the micromirror contacts a correspondingly lower landing element (e.g., the spring tip 204 described herein). The spring tip 204 may be lifted by a support (e.g., support 210) coupled to a substrate 208. The spring tip 204 may flex in response to a micromirror landing on the spring tip 204 (e.g., by flexing to absorb and store energy).

[0038] Spring tip 204 may include a corresponding contactor spring (e.g., contactor spring 912, referred to herein). Figure 9 (Description). A contactor spring 912 extends distally from a support element (e.g., support member 210). The contactor spring 912 includes a proximal portion 914 (e.g., a first portion) and a distal portion 916 (e.g., a second portion). The contactor spring 912 includes a cavity (e.g., formed using a curved surface), wherein the cavity includes the distal portion (e.g., the second portion, which may be shaped like the end of a hook). The distal portion of the cavity includes an increasing inclined surface extending away from the substrate (e.g., such that the clearance from the spring tip 204 to the substrate 208 widens as the inclined surface extends away from the proximal portion). The spring tip 204 includes a first contact surface adjacent to (e.g., adapted to contact) the vertical terminal surface of the distal portion.

[0039] As described below, gray scale lithography can be used to form example mechanical elements such as contactor springs. Examples of gray scale lithography are described in U.S. Patent No. 9,864,188, issued January 9, 2018, entitled Operation / Margin Enhancement Feature for Surface-MEMS Structure; Sculpting Raised Address Electrode, the entirety of which is incorporated herein by reference.

[0040] Each pixel modulator element in the array of pixel modulator elements can include two pairs of spring tips 204 (e.g., where each spring tip 204 includes Figure 9 a contactor spring 912 of FIG. 1) and a micromirror 201. The micromirrors in the array of micromirrors each include a second contact surface (e.g., a first contact surface for contacting a respective spring tip 204). The respective micromirror is adapted to move in a first direction to push the first and second contact surfaces together; and is adapted to move in a second direction to push the first and second contact surfaces apart.

[0041] In another example, the spring tips 204 are adapted to move in a first direction to push the first and second contact surfaces together, and the spring tips 204 are adapted to move in a second direction to push the first and second contact surfaces apart.

[0042] The electrical drive electrodes 205 and 206 electrostatically push (e.g., apply a force to facilitate movement, attempt movement, and / or hold) the micromirror 201 toward either of two operating positions. The electrodes 205 and 206 are formed over a substrate such that a portion (e.g., a partial portion or an entire portion) of the respective micromirror is formed over one of the electrodes 205 and 206. The electrodes 205 and 206 are coupled to respective memory cells to electrostatically position the respective micromirror in response to a logic state latched by the memory cell. Thus, in response to respective memory cells coupled to the electrodes 205 and 206, the respective micromirror of a selected pixel modulator element in the array of pixel modulator elements can be electrostatically positioned by the respective electrode (e.g., 205 or 206). In response to an electrostatic field distributed by a first electrode, the respective micromirror is adapted to move in a first direction, and in response to an electrostatic field distributed by a second electrode, the respective micromirror is adapted to move in a second direction.

[0043] Adjacent (e.g., below) the micromirrors 201 are memory cells 207 containing circuitry, e.g., CMOS memory elements. The memory cells 207 contain circuitry formed on a substrate 208, where the circuitry is arranged to electronically latch a logic state suitable to indicate a selected one of the first and second directions (e.g., where the circuitry is suitable to control the physical state of the micromirror 201 in response to the logic state of the respective memory cell 207). The electronic state of the pixel memory cell at least partially determines the mechanical position of the micromirror.

[0044] In examples, toggling the content of a memory cell does not necessarily cause an immediate change in the mechanical state of the respective micromirror. In examples, a "reset" signal is asserted, causing the immediate (e.g., current) state of the CMOS memory cell to be transferred to the electrode controller to mechanically position the micromirror to the state latched by the respective CMOS memory cell. Assertion of the reset signal releases the micromirror to be in a neutral position, such that the micromirror can be advanced from the neutral position to re-land in one of two positions that can be determined by the state of the coupled CMOS memory cell. The reset operation can assert the reset signal such that a selected group of pixels can be individually preloaded over a period of time, and a selected group of micromirrors can change their respective mechanical positions in synchrony (e.g., in response to a commonly asserted command signal).

[0045] An example DMD can be fabricated as a MEMS assembly containing an array of peripheral and non-peripheral aluminum micromirrors formed over a substrate 208. The non-peripheral positioned micromirrors of the example array can be controlled to rotate in response to digital information electronically latched in CMOS circuitry of the substrate 208, while the peripheral positioned micromirrors can be arranged to rotate (e.g., not in response to latched memory states) to a selected default position (e.g., to deflect light over the periphery of the MEMS assembly, which can otherwise reduce the contrast ratio of a projected image).

[0046] Such peripheral positioned micromirrors (e.g., which can be referred to as border micromirrors or "ponds") are formed around the perimeter of a central core of active micromirrors in an array. The border micromirrors are not necessarily user addressable, and can automatically tilt to a -12 degree off position in response to application of power to the device. An example implementation has a border micromirror width of 10 border micromirrors on the outer perimeter (e.g., edge) of an array arranged with 912 rows by 1140 columns of active micromirrors. The border micromirrors can be used to direct stray incident light outside of the field of view of the projected light path.

[0047] Figure 3The diagram shows a cross-section taken along the diagonal hinge axis of an example pixel element. In the cross-section of example pixel element 300, the MEMS micromirrors at the pixel location are formed as an upper structure above a silicon substrate that has been processed using CMOS fabrication processes to form a memory array and other circuitry. The CMOS circuitry includes transistors (e.g., formed using doped silicon), electrical contacts, and interconnects formed in two patterned metal layers called "Metal 1" (M1) and "Metal 2" (M2). Contacts to the underlying CMOS circuitry (e.g., ...) can be formed by the deposition and patterning of a third conductive layer called "Metal 3" (M3). Figure 2 The via 2 contact (to CMOS), metal address pads, and bias / reset bus elements are included. A first photoresist layer (e.g., comprising a photoresist) may be formed and patterned over the patterned conductive layer M3. The patterned conductive layer M3 includes via openings (e.g., openings for vias).

[0048] The hinge forming material layer may include at least one layer of metal referred to as "metal 4" (M4), which is formed over a patterned first photoresist layer and patterned to form... Figure 2 The torsion spring 203 and various spring tips 204 and electrodes 205 (e.g., raised address electrodes). Hinge forming material conformally extends into the through-hole opening to define a support 210 for the hinge and for the raised electrode. Figure 2 (The "SPI via" in the image).

[0049] A metal layer, referred to as "metal 5" (M5), containing a central via opening, can be formed by forming and patterning a second photoresist layer (e.g., comprising a photoresist) over a patterned hinge forming layer M4. The metal layer M5 comprises at least one metal layer, referred to as "metal 5" (M5), formed over the patterned second photoresist layer and patterned to form a reflective element (e.g., a rectangular micromirror). Mirror forming material extends into the via to define a connector support for the micromirror (e.g., mirror via 211). To provide a flat surface for subsequent CMOS-related fabrication processes, the second photoresist layer is planarized prior to the deposition of the mirror forming material. The first and second photoresist layers initially provide support for the hinge and mirror forming layer during fabrication and are subsequently removed after formation to release (e.g., by etching away the underlying temporary support structure) the hinge and micromirror.

[0050] Figure 4 and Figure 5 These are example micromirrors, each with a tilt angle of up to 12 degrees. Figure 2A front projection view and an elevation view of an example pixel structure. In response to asserting a reset signal to an "on" (+12 degrees) or "off" (-12 degrees) position, micromirror 201 can be urged (e.g., by applying an electrostatic force) to tilt. The reset signal can be asserted in response to a logic state (e.g., a logic 1 or logic 0 stored as a capacitive storage or electronically latched) stored in an underlying CMOS memory cell.

[0051] In one example, an array of micromirrors can be electrostatically and independently urged to a selected one of an on or off position. Asserting the output of each memory cell (e.g., a logic 1 or logic 0 corresponding to a bit plane bit for a corresponding pixel position) and its complement output differentially energizes (e.g., by coupling opposite potentials) a selected one of respective electrodes 205 and 206. Electrodes 205 and 206 can be disposed adjacent (e.g., below) a micromirror on respective (e.g., opposite) sides of a hinge axis.

[0052] In response to applying a sufficient bias / reset potential to a selected one of electrodes 205 and 206, micromirror 201 rotates about its hinge axis in response to electrostatic attraction of the electrode having the greatest potential difference (e.g., voltage difference relative to the bias / reset potential). In response to micromirror 201 being tilted (e.g., rotated), micromirror 201 contacts (e.g., lands on) spring tip 204 adjacent (e.g., proximate) to the energized electrode, which helps prevent micromirror 201 from contacting the selected (e.g., energized) electrode, and which helps preload a mechanical force for releasing the micromirror (e.g., under stored spring action energy). In a configuration where the bias / reset potential is removed (e.g., by floating / tri-stating or differentially setting the electrode pair to 0 volts), micromirror 201 returns to a flat state (e.g., neutral, intermediate position) in response to the mechanical force stored in torsion spring 203 and spring tip 204 being flexed (e.g., preloaded).

[0053] The energy stored by spring tip 204 and torsion spring 203 is combined to help overcome stiction that can occur between the contact surface of micromirror 201 and spring tip 204 at contact surface 501. As described below with respect to Figure 9 Spring tip 204 (e.g., spring tip 900) can include a contactor spring 912 having a distal portion 916 that can increase a contact angle between contact surface 501 of spring tip 204 and a contact surface (e.g., substrate side) of micromirror 201 (e.g., for reducing a space in which condensation and capillary action can occur). Contact surface 501 is a terminal portion of a distal surface of spring tip 204 that contacts (e.g., physically contacts) a portion of a surface of micromirror 201. Contact surface 501 can be flat or rounded (e.g., such that a reduced contact point of a rounded curve is adapted to contact micromirror 201).

[0054] In Figure 9 the example shown in FIG. 8, spring tip 204 (e.g., spring tip 900) can include an extension arm 910 including a first surface (e.g., 920 of FIG. 9) proximate a substrate (e.g., M3) and including a second surface (e.g., 922 of FIG. 9) proximate a second element (e.g., micromirror 210). A contact spring 912 includes a third surface (e.g., including a number of surface points 932 having a radius R concentrated at a surface point 932) proximate the second element (e.g., micromirror 201). A first distance from a first point of the second surface to the second element is less than a second distance from a second point (e.g., surface point 932 of FIG. 9) of the third surface to the second element (e.g., micromirror 201). In configurations where the first contact surface (e.g., 501) and the second contact surface are separated, the first distance is less than the second distance. Figure 5 Figure 9 Figure 9 Figure 9

[0055] In a geometric example of an example pixel structure, a vertex (e.g., the rightmost corner) of right triangle 530 includes an angle 531 that can otherwise be created, for example, when a longitudinal axis of upper surface 920 (e.g., micromirror side) of extension arm 910 is conceptually extended to intersect with a lower (e.g., substrate side) surface of tilted micromirror 201. In examples, right triangle 532 is a similar triangle (e.g., such that corresponding angles of right triangles 530 and 532 have the same value) with respect to right triangle 530. A vertex (e.g., the rightmost) of right triangle 532 includes an angle 533 created between contact surface 501 and the substrate side (e.g., lower) surface of tilted micromirror 201.

[0056] According to geometric principles, angle 533 is complementary to angle 531, such that given a 12 degree micromirror tilt, angle 531 is 12 degrees and angle 533 is 72 degrees. The increase in angle 533 of the contact (e.g., from 12 degrees to 72 degrees) decreases the proximity of spring tip 204 and micromirror 201 around the proximate surfaces. The decrease in area around the contact surface decreases the area in which meniscus / capillary formation can occur (e.g., such that stiction can be reduced), as described below with respect to Figures 6A to 6C

[0057] Figure 6A ​​​​​A capillary condensation model is shown that includes a flat surface (e.g., planar surface) adjacent to a curved surface. The capillary can form in a non-UHV space in a top space of a MEMS package used to encapsulate a MEMS device. The MEMS top space can include water and other condensable / mobile species that can condense on surfaces in and around the MEMS top space. The spring tip 204 described herein can mechanically store energy (e.g., by deflecting a curved leaf spring / leaf spring in response to forces encountered in response to tilting a micro-mirror in response to contact), such that the stored energy can be released later to help offset the adhesive energy associated with capillary condensation. The adhesive energy associated with capillary condensation can be described with reference to the Laplace pressure expression, which is given herein as:

[0058] Δp = (-2πR)(dγ L / r1) (1)

[0059] where R is the radius of the surface 641 (e.g., curved and / or spherical surface) adjacent to the flat (e.g., planar) surface 642. The term dγ L / r1helps to indicate the degree to which a radius r1 of a meniscus is formed (e.g., the meniscus shape is formed) around the mechanical contact, and the term helps to indicate the associated distance that the meniscus r1 rises up on the sphere (d) as well as the interfacial energy (γ L ) of the capillary. The term -2πR is related to the geometry of the spherical surface, and is negative, which indicates that the meniscus force is an attractive force.

[0060] There is a direct relationship between (a) the meniscus / capillary interaction force; and (b) the radius (R) of the surface 641. A smaller radius results in a smaller capillary, which results in an accompanying smaller interaction force. There can be similar forces between two conceptual spheres, such that a smaller radius of curvature of two spheres can result in a smaller meniscus / capillary and a reduced attraction force therebetween.

[0061] Figure 6BCapillary condensation that can occur between two instances of MEMS elements is demonstrated, e.g., a micro-mirror 601 leaning against a spring tip 604 (e.g., resting on the spring tip 604). A meniscus 646 (e.g., which can be a meniscus of a swing ring of water or other condensable mobile species) moves a condensable and progressively builds up in the intervening interstitial space between the micro-mirror 601 and the spring tip 204. The topology of the spring tip 604 limits (e.g., reduces) adhesion created by the surface tension of the meniscus 646 that can otherwise occur between the micro-mirror 601 and the spring tip 604. The adhesion enhanced by the meniscus 646 is less than, e.g., adhesion enhanced by a "wedge" of condensate that can otherwise form in response to an extended arm of the spring tip 604 coming sufficiently close (e.g., such that capillary action occurs therebetween) to the micro-mirror 201.

[0062] Figure 6C Capillary condensation that can occur between two instances of MEMS elements is demonstrated, e.g., a protrusion (e.g., a reduced contact 620) of an element 651 (e.g., a micro-mirror) leaning against a spring tip 654. An example reduced contact is a protrusion feature arranged to increase the play (e.g., height or separation distance) between adjacent surface areas of the elements 651 and 654. Increasing the play helps to reduce the surface tension of a meniscus because the radius of the meniscus decreases (e.g., decreases as a function of changes in the lift) in response to drawing a condensable in a direction (e.g., downward) in response to a force to push the spring tip 654 in the direction (e.g., downward) and away from the element 651. Decreasing the radius of the condensable can also decrease the amount of adhesion between the two elements 651 and 654.

[0063] Figure 7 is Figure 2 A perspective top view of an example pixel modulator element. The pixel modulator element 200 includes a protrusion 720 (e.g., a reduced contact) formed on a substrate side (e.g., bottom) side of a micro-mirror 201. The protrusion 720 is adapted to reduce a contact area (e.g., a contact surface 501) that can otherwise occur between the substrate bottom side of the micro-mirror 201 and at least one of the protrusion spring tip 204. Other examples of protrusions are described herein, e.g., the contact surfaces 846, 847, and 849 of FIG. 8.

[0064] The protrusions 720 can be formed in a suitable shape with a curvature (e.g., a significant curvature). In the perspective view, the protrusions 720 are shown as linear wedges or "ribs" with rounded edges of the wedges forming a reduced contact surface due to a low radius of curvature (ROC). The protrusions 720 can each include a long axis that is oblique (e.g., skewed) with respect to a long axis of the corresponding contact surface 501. In another example, the protrusions 720 can be an elliptical cap or an array of elliptical caps. In yet another example, the protrusions on the substrate side (e.g., underside) of the micromirror 201 can contact a rounded surface extending from a terminal surface (e.g., contact surface) of the spring tip 204. Other examples can include other shapes and configurations of protrusion features with small contact areas between movable elements and another element in a MEMS device. Reducing the contact surface can include sub-resolution features patterned with gray scale lithography.

[0065] In Figure 7 the example shown in FIG. 7, the ROC (radius of curvature) of the contact surface of the protrusions 720 can be less than 1 pm. In some examples described herein, a reduction in stiction can be obtained, for example, with protrusion features having a contact surface with a ROC between 0.2 um and 10 um.

[0066] Figures 8A to 8K is a cross-sectional view showing formation of an example reduced contact surface of an example spring tip. Figures 8A to 8K Examples of FIG. 8 show fabrication of a reduced contact surface of a spring tip 204 for contacting a bottom side of a micromirror 201.

[0067] Further, the described reduced contact surfaces (e.g., contact surfaces such as the spring tip 204) are not limited to contacting micromirrors of a DMD device. The reduced contact surfaces are suitable for application to various movable elements included by DMDs as well as other MEMS devices, where small contact surfaces can reduce stiction forces between moving MEMS elements. (e.g., the drawings are not necessarily drawn to scale for simplicity.)

[0068] In Figure 8A , the example CMOS substrate 208 has been fabricated as an example result of semiconductor processing operations to form circuitry and memory cells, as described above with reference to Figure 2 and 3 The support 210 has been fabricated by a process including a photoresist layer (which has been removed) such as a photoresist suitable for forming cavities for forming the support 210.

[0069] Figure 8BThe formation of an example photoresist layer 820, such as a photoresist spacer layer, is described. The photoresist layer 820 is deposited on the upper surface of the substrate 208. The photoresist layer 820 includes a depth to provide vertical clearance (e.g., vertical play) for the next level of elements (e.g., spring tips 204 (e.g., as described below)) of the MEMS to be formed.

[0070] Figure 8C An example gray scale mask 821 is described that is patterned to expose selected portions of the photoresist layer 820 to light 822, which can be focused energy, such as ultraviolet (UV) or other short wavelength radiation. The photoresist layer 820 is exposed to the light 822 through the gray scale photolithography mask to form cavities in the upper surface of the photoresist layer 820. The gray scale photolithography process can include a sub-resolution, two-dimensional binary optical mask that is illuminated by a photolithography stepper system adapted to locally modulate the intensity of the UV light or other focused radiation (e.g., to form the cavities 823, described below with respect to Figure 8D described).

[0071] The modulated intensity of the light 822 (e.g., modulated by the sub-resolution features of the gray scale mask 821) exposes the photoresist to selected gradients and depths. The curvature gradient of the cavities includes a change in depth that is less than the wavelength of the light used to pattern the photoresist layer 820. For example, the cavities 823 and 824 (e.g., which can be precursor structures for shaping the contactor springs) include a design feature (e.g., a change in the depth of curvature (e.g., the curvature gradient)) that is less than the length of the wavelength of the energy applied to pattern the photoresist layer through which the cavities are formed.

[0072] After the exposed photoresist is developed, a gradient height profile is formed in the currently remaining portions of the photoresist layer 820 (e.g., as formed by the gradient exposure depths). For example, the design feature can be a change in the depth of curvature (e.g., the gradient) of the upper surface of the cavity, where at least one point of the curvature is closer to the substrate (e.g., 208) than other points of the curvature (e.g., the design feature can be adapted to form a sloped surface of the cavity 918 shown in FIG. 9B, such as the surface point 932). Figure 9

[0073] The gray scale mask 821 can be designed with sub-resolution features adapted to achieve diffraction of the UV light of the optical photolithography process. Different opaque sub-resolution feature sizes can be included to create different diffraction patterns (e.g., for forming sub-resolution features in the underlying photoresist). In the configuration of the optical lens system of the photolithography stepper that the different diffraction patterns are run through, the different diffraction patterns are converted into different intensity levels (e.g., so that different depths of the exposed photoresist are formed).

[0074] ​The different sizes of the opaque sub-resolution features of the gray scale mask 821 can be referred to as gray scale levels, where each level (of gray scale levels) of the gray scale mask 821 is adapted to change the intensity of the light 822 by a selected amount. Gray scale lithography techniques allow for the formation of curved surfaces (e.g., of the spring tip 204, having a radius of R, where the depth of the curved surface changes by less than the wavelength of the light 822 applied to fabricate the pixel modulator element 200. Figure 9

[0075] To produce different gray scale levels, the size (e.g., width) of the opaque features can be changed while remaining within the set pitch. Generally, the smaller the opaque features, the greater the amount of intensity of the light 822 traveling through the optical lens system onto the photoresist layer 820.

[0076] Figure 8D A first set of example cavities is illustrated. After the exposed photoresist layer is developed, cavities 823 and 824 can be formed in the photoresist layer 820. In configurations where a positive resist is used, due to the exposure of the light 822, the exposed portions of the photoresist layer 820 are softened and are washed away during the development process. In configurations where a negative resist is used, due to the exposure of the light 822, the exposed portions of the photoresist layer 820 are hardened and the unexposed portions are washed away during the development process (photographic negative of the pattern being transferred is used in conjunction with the negative resist).

[0077] In examples, the gradient and depth of each of the cavities 823 and 824 can be controlled by the exposure time and intensity of the light 822. The cross-section of the cavities 823 and 824 can be cylindrical. The cavities 823 and 824 are shaped to form the surface (e.g., lower surface) of the respective spring tip 204 cavity (see, e.g., cavity 918 of the contactor spring 912 of Figure 9 Other cavity shapes (e.g., a “v” shaped cavity) can be fabricated to form spring tip 204 cavities of other shapes.

[0078] Figure 8E ​An example spring tip 204 is shown formed by depositing a deformable metal layer over cavities 823 and 824 of photoresist layer 820. Spring tip 204 can be formed by depositing a deformable metal layer over cavities 823 and 824 formed in an upper surface of photoresist layer 820, such that the deformable metal layer includes an upper surface having cavities that follow (e.g., are conformal with) the gradient profile of cavities 823 and 824. Cavities 918 (e.g., contact spring cavities) of the deformable metal layer can be formed according to the profile (e.g., cavities 823 and 824) formed in the exposed surface of photoresist layer 820. For example, cavities in the upper surface of the photoresist layer are arranged to form spring tip 204 that includes a reduced contact surface at a distal end of the cavities of spring tip 204 (e.g., about a proximal support end of spring tip 204).

[0079] Figure 8F An example spring tip 204 is shown after removal of photoresist layer 820. Photoresist layer 820 is a sacrificial layer that is removed to form an air gap between spring tip 204 and substrate 208. Support 210 supports (e.g., cantilevered supports) a proximal end of spring tip 204 such that a contact surface on a terminal end of spring tip 204 (e.g., adjacent a contact micro-mirror) is free (e.g., has sufficient play) to flex (e.g., flex downward) toward substrate 208 in response to a force applied by the contact micro-mirror.

[0080] The cavities of spring tip 204 are adapted to form a contact with a reduced contact surface area, which reduces stiction between spring tip 204 and micro-mirror 201. The cavities of spring tip 204 also increase the effective mechanical length (though not necessarily the total length) of the range of spring tip 204, such that spring tip 204 can absorb and store additional energy (e.g., in a flexed portion of spring tip 204) by flexing along the spring tip cavities in response to a "hit" by impact, contact micro-mirror 201.

[0081] For example, the cavities of spring tip 204 are adapted to convert energy received from a micro-mirror into stored energy during a first movement in a first direction, and to release the stored energy during a second movement of the micro-mirror in a second direction (e.g., such that the released stored energy is generated from the stored energy received from the micro-mirror during the movement in the first direction). The increase in stored energy (e.g., stored in a flexed portion of spring tip 204) provides additional energy density for overcoming stiction between spring tip 204 and micro-mirror 201. The increase in stored energy density may, for example, allow for a smaller pitch (e.g., a greater number per unit area) of micro-mirrors 201 in a pixel modulator element 200.

[0082] The lower surface of the cavity of the spring tip 204 is adapted to form a reduced contact surface adjacent to the substrate 208. In examples where heat is applied (e.g., heat applied during a subsequent manufacturing process or during operation, for example) to a device containing the spring tip 204, the spring tip 204 can sag (e.g., in response to a temperature rise of the spring tip 204) and come into contact with an adjacent surface (e.g., an upper surface of the substrate 208). In response to the spring tip 204 contacting the upper surface of the substrate 208, stiction can draw the spring tip 204 against the substrate, which can result in a "stuck" pixel. The lower curved surface of the cavity of the spring tip 204 contains a reduced contact surface that reduces stiction that can otherwise occur (e.g., as described above with respect to Figure 6A

[0083] In various examples, the reduced contact surface is coupled to a planar surface of an element (e.g., a portion of the spring tip 204, the micro-mirror 201, and / or the torsion spring 203), where the planar surface is adjacent to (e.g., above) a lower surface of the substrate 208, and where there is a gap between the reduced contact surface and the substrate. The reduced contact surface extends from the planar surface (e.g., the spring tip 204, the micro-mirror 201, and / or the torsion spring 203) and toward the substrate. Various reduced contact surfaces can be formed as protrusions arranged in various patterns (e.g., arranged under selected suspended elements or in a linear or grid pattern) to reduce a contact surface area that can otherwise occur under conditions that cause swelling (e.g., thermal swelling) of the deformable metal elements of the pixel modulator element 200.

[0084] In Figure 8G , an example spring tip 204 is shown after being encapsulated by a photoresist layer 840. The photoresist layer 840 contains support spacers of a selected thickness that are adapted to form a vertical clearance (e.g., play) sufficient to allow for free movement during operation of a next level element of the MEMS (e.g., the micro-mirror 201 to be formed as described below).

[0085] Figure 8H A cross-sectional view of an example grayscale mask 841 that is patterned to expose selected portions of the photoresist layer 840 in response to illumination by light 842 (e.g., which can be UV or another frequency of short wavelength radiation) is shown. The grayscale lithography process exposes the photoresist layer 840 to form a gradient (e.g., for defining a curved cavity surface) of a selected depth of the reduced contact surface (e.g., the protrusion contact surfaces (e.g., 846 and 847) of the micro-mirror 201 and, for example, the auxiliary hinge support 849, as described below). After the exposed photoresist is developed (and removed), the gradient height profile of the patterned photoresist (e.g., which is engraved top surface) is preserved (e.g., as patterned in response to the grayscale mask 841). ​

[0086] Figure 8I A second set of example cavities is shown. Cavities 839, 843, and 844 can be formed in photoresist layer 840 after etching the exposed photoresist layer (e.g., in examples where photoresist layer 840 includes a positive photoresist). Exposed portions of photoresist layer 840 are softened by exposure to light 842 and washed away during a development process. In examples, the depth (e.g., curvature and degree of curvature) of cavities 839, 843, and 844 can be controlled by exposure time and intensity of light 842. Cavities 839, 843, and 844 can be cylindrical segments suitable for shaping protruding contact surfaces, such as 846 and 847 of micromirror 201, and such as auxiliary hinge support 849. Other cavity shapes can be suitable for shaping additional types of protrusions of metal layer 845 deposited later.

[0087] Figure 8J An example metal layer 845 deposited on the exposed (e.g., upper) surface of photoresist layer 840 is shown, such that metal layer 845 is conformal with cavities 839, 843, and 844. Metal layer 845 includes a deformable metal that can be patterned and etched using fabrication techniques to form a MEMS element, such as micromirror 201, as described below with reference to Figure 8K

[0088] Figure 8K An example micromirror 201 is illustrated after removal of photoresist layer 840 and patterning and etching of metal layer 845 (e.g., as a completed micromirror). Micromirror 201 includes protruding contact surfaces 846 and 847 configured to contact spring tip 204 in response to micromirror 201 moving (e.g., tilting) to the right or to the left (e.g., rotating clockwise or counterclockwise about pivot axis 848). Pivot axis 848 extends longitudinally through torsion spring 203 and intersects a central axis of support 210 (e.g., suitable for supporting torsion spring 203, as shown in a front projection view in Figure 2

[0089] Auxiliary hinge support 849 is an example of a reduced contact surface. Auxiliary hinge support 849 is included by (e.g., coupled to) torsion spring 203, which is suitable for moving about torsion spring 203 in a first direction (e.g., open) and a second direction (e.g., closed). Auxiliary hinge support 849 can be a downwardly extending protrusion of torsion spring 203 (and / or an upwardly extending protrusion of underlying substrate 208, not shown). Auxiliary hinge support 849 is arranged to reduce a contact area (e.g., and an area adjacent to the contact area) that can occur between torsion spring and a corresponding contact surface (e.g., a reduced contact surface) formed on an adjacent surface of an underlying substrate (e.g., substrate 208), as described above with reference to Figures 6A to 6C ​​Description).

[0090] In examples, the subsequent manufacturing process and / or device operation can include the application of heat, which can be absorbed by the completed torsion spring 203, causing the torsion spring 203 to expand (e.g., longitudinally expand). The expansion of the torsion spring 203 can cause the torsion spring to sag, such that a portion of the torsion spring 203 (e.g., the secondary hinge support 849) moves, contacts, and potentially adheres to an underlying structure (e.g., the substrate 208). Stiction can occur at the contact surface of the torsion spring 203 and the substrate 208 (e.g., described with reference to surfaces 641 and 642 of FIG. 6B). Figure 6A

[0091] As described herein, stiction is reduced from a level that can otherwise occur without the described secondary hinge support 849, where such a level can result in a permanent adhesion of the torsion spring 203 (e.g., adhered by the stiction itself, and / or adhered by a top space reactive chemical species introduced as the stiction binds the torsion spring 203 to the substrate 208). The permanent adhesion can result in a permanent visible pixel defect of the display system 100. In various examples, the secondary hinge support 849 can be formed between the micromirror 201 and the torsion spring 203, and / or between the torsion spring 203 and the substrate 208.

[0092] Figure 9 An example reduced contact surface of an example spring tip is shown. As described herein, the spring tip 900 can be (or include) the spring tip 204. The spring tip 900 is an element that can include an extender arm 910 (e.g., which can be a flat leaf spring) and a contactor spring 912 (e.g., which can be a curved leaf spring).

[0093] The extender arm 910 is coupled between the contactor spring 912 and a support (e.g., 210 coupled to the substrate 208), such that there is a gap (e.g., an air gap) between the spring tip 900 and the substrate. In operation, the spring tip 900 (including the extender arm 910 and the contactor spring 912) flexes into the gap (e.g., downward) in response to contact by the substrate side (e.g., lower) contact surface of the tilted micromirror 201. Thus, the extender arm is adapted to convert energy received from the micromirror during a first movement in a first direction into stored energy, and to release the stored energy during a second movement in a second direction.

[0094] ​The contactor spring 912 includes a first portion (e.g., a proximal portion) coupled to the support (e.g., by the extension arm 910) and includes a second portion (a distal portion) that includes a cavity 918 having a sloped surface (e.g., an upper sloped surface and / or a lower sloped surface). The first portion is coupled between the support and the second portion. As the sloped surface extends away from the first portion, a clearance from the sloped surface to the substrate widens, and the second portion includes a first contact surface 501 (e.g., that is adapted to contact a surface of the micromirror) proximate (e.g., distally proximate) the sloped surface.

[0095] The spring tip 900 includes an upper surface 920 proximate a micromirror (which is arranged to overlie the spring tip 900) and includes a lower surface 922 proximate a substrate. A centerline 926 conceptually extends from a proximal portion of the spring tip 900 through a distal portion of the spring tip 900. In a configuration in which the spring tip 900 is separated from the micromirror (e.g., in a neutral position), there is a clearance (e.g., a distance or height) from a portion (e.g., a point) of the upper surface 920 to the micromirror that is less than a clearance from a portion (e.g., a surface point 932) of the cavity 918 to the micromirror. In a configuration in which the spring tip 900 is in contact with the micromirror (e.g., at the time of landing of the micromirror, as shown in FIG. 6B), there is a clearance (e.g., a distance or height) from a portion of the upper surface 920 to the micromirror that is less than a clearance from a portion (e.g., a surface point 932) of the cavity 918 to the micromirror. Figure 5 In a configuration in which the spring tip 900 is in contact with the micromirror (e.g., at the time of landing of the micromirror, as shown in FIG. 6B), there is a clearance (e.g., a distance or height) from a portion of the upper surface 920 to the micromirror that is less than a clearance from a portion (e.g., a surface point 932) of the cavity 918 to the micromirror.

[0096] The upper surface 920 extends horizontally along the extension arm 910 (e.g., extends left to right as illustrated): in the proximal portion 914 of the contactor spring 912, the upper surface 920 extends downward (toward the substrate) along an increasing curvature of the cavity 918; and in the distal portion 916 of the contactor spring 912, the upper surface 920 (e.g., a height of the upper surface 920) extends upward and away from the substrate. The contactor spring 912 includes (e.g., at a distal end includes) a contact surface 501. The contact surface 501 is a terminal portion of the spring tip 204 that is proximate the cavity 918 formed by the proximal portion 914 and the distal portion 916. The contact surface 501 is adapted to increase a contact angle between the contact surface 501 of the spring tip 900 and a lower surface of the micromirror 201 (e.g., to reduce an area in which condensation and capillary action can occur). The contact surface 501 is a reduced contact feature for reducing stiction, as described above with respect to FIGS. 5A-5B. Figures 6A to 6C

[0097] ​In cross-section view, the sloped surface of the cavity 918 can be curved (e.g., have surface points 932 spaced a radius R from a focal point 930), notched (e.g., "v" shaped), or trapezoidal (e.g., formed anisotropically), or straight (e.g., formed isotropically). The sloped surface of the cavity 918 is arranged: such that a clearance from the sloped surface of the distal portion 916 to the substrate widens (e.g., increases) as the sloped surface extends away from the proximal portion 914 (e.g., as projected over an increasingly distal portion); and such that the distal portion includes a first contact surface adjacent the sloped surface. In various examples, the surface points 932 (of the upper surface of the cavity 918) can be: lower than a portion of the upper surface 920 of the extension arm; lower than a portion of the centerline 926 of the extension arm; and / or lower than a portion of the lower surface 922 of the extension arm.

[0098] In an example method, a reduced contact surface for a MEMS device can be formed as described herein. The example method includes: depositing a photoresist layer adjacent a first surface of a substrate; forming a first cavity in a surface of the photoresist layer; depositing a deformable metal layer adjacent the surface of the photoresist layer, wherein the deformable metal layer includes a second cavity formed adjacent the first cavity, and wherein the deformable metal layer includes a first contact surface; etching the deformable metal layer to form a spring tip including the second cavity; removing the photoresist layer to form a gap between the spring tip and the substrate; and forming a micromirror adjacent the second cavity, the micromirror including a second contact surface positioned over the first contact surface; wherein the micromirror is adapted to move in a first direction to close the first and second contact surfaces; and wherein the micromirror is adapted to move in a second direction to open the first and second contact surfaces.

[0099] The example method optionally includes at least one of: forming a memory cell on the substrate, wherein the memory cell includes circuitry adapted to electronically latch a logic state indicative of a selected one of the first and second directions, wherein the spring tip and the micromirror are formed over the memory cell; and forming an electrode over the substrate, wherein the micromirror is formed over the electrode, and wherein the electrode is adapted to electrostatically position the micromirror in response to the logic state latched by the memory cell.

[0100] Modifications of the described embodiments are possible, and other embodiments are possible. Within the scope of the claims, modifications can be made to the embodiments described.

Claims

1. An apparatus comprising: a substrate; a first post coupled to the substrate; a hinge layer including: a torsional hinge coupled to the first post; and a spring tip coupled to the torsional hinge; a second post coupled to the torsional hinge; and a mirror coupled to the second post, the mirror having a second contact surface, the spring tip having a first contact surface, a first surface facing the mirror, a second surface facing the substrate, and a third surface facing the mirror, wherein a first distance from a first point of the second surface to the mirror is less than a second distance from a second point of the third surface to the mirror.

2. The apparatus of claim 1, wherein the spring tip is configured to convert received energy into stored energy when the second contact surface contacts the first contact surface, and to release the stored energy when the second contact surface is separated from the first contact surface.

3. The apparatus of claim 1, wherein the spring tip includes an extension arm and a contactor spring portion, the extension arm coupling the contactor spring portion to the torsional hinge.

4. The apparatus of claim 3, wherein the spring tip is configured to convert received energy into stored energy when the second contact surface contacts the first contact surface, and is configured to release the stored energy when the second contact surface is separated from the first contact surface.

5. The apparatus of claim 3, wherein the contactor spring portion is hook-shaped.

6. The apparatus of claim 3, wherein the contactor spring portion is curved, notched, trapezoidal, or straight.

7. The apparatus of claim 1, wherein the first distance is less than the second distance when the first contact surface is separated from the second contact surface.

8. The apparatus of claim 1, further comprising a memory cell in the substrate, wherein the mirror is configured to reflect light in response to a memory state of the memory cell.

9. The apparatus of claim 1, wherein the second contact surface is on a protrusion of the mirror.

10. The apparatus of claim 1, the hinge layer further including first and second electrodes, wherein the mirror is configured to move in a first direction in response to a first voltage on the first electrode, and wherein the mirror is configured to move in a second direction in response to a second voltage on the second electrode.

11. A microelectromechanical system device comprising: a hinge layer including: a torsional hinge; and a spring tip coupled to the torsional hinge, the spring tip including a contactor spring portion and an extension arm, the extension arm between the contactor spring portion and the torsional hinge, the contactor spring portion having a first contact surface, wherein the contactor spring portion is curved; a mirror, the mirror having a second contact surface, the second contact surface configured to contact the first contact surface, and the second contact surface configured to separate from the first contact surface; and a post coupled to the mirror and the torsional hinge. ​ ​ 12. The microelectromechanical system device of claim 11, wherein the contactor spring portion has a cavity.

13. The microelectromechanical system device of claim 11, wherein the contactor spring portion is a curved leaf spring.

14. The microelectromechanical system device of claim 11, wherein the mirror comprises a protrusion, the second contact surface being on the protrusion.

15. The microelectromechanical system device of claim 11, wherein the first contact surface is at an end of the contactor spring portion.

16. The microelectromechanical system device of claim 11, wherein the post is a first post, the microelectromechanical system device further comprising: a substrate; and a second post coupling the torsional hinge to the substrate.

17. The microelectromechanical system device of claim 16, wherein the substrate comprises a complementary metal-oxide-semiconductor (CMOS) memory cell, and the hinge layer comprises an electrode, the electrode being over the CMOS memory cell.

18. A method comprising: depositing a photoresist layer adjacent a first surface of a substrate; forming a first cavity in a surface of the photoresist layer; depositing a deformable metal layer adjacent the surface of the photoresist layer, wherein the deformable metal layer includes a second cavity formed adjacent the first cavity, and wherein the deformable metal layer includes a first contact surface; etching the deformable metal layer to form a spring tip including the second cavity; removing the photoresist layer to form a gap between the spring tip and the substrate; and forming a micro-mirror adjacent the second cavity, the micro-mirror including a second contact surface positioned over the first contact surface; wherein the micro-mirror is configured to move in a first direction to close the first and second contact surfaces; and wherein the micro-mirror is configured to move in a second direction to open the first and second contact surfaces, wherein the spring tip has a first surface facing the mirror, a second surface facing the substrate, and a third surface facing the mirror, wherein a first distance from a first point of the second surface to the mirror is less than a second distance from a second point of the third surface to the mirror.

19. The method of claim 18, further comprising: forming a memory cell on the substrate, wherein the memory cell includes circuitry configured to electronically latch a logic state indicating a selected one of the first and second directions, wherein the spring tip and the micro-mirror are formed over the memory cell.

20. The method of claim 19, further comprising forming an electrode over the substrate, wherein the micro-mirror is formed over the electrode, and wherein the electrode is configured to electrostatically position the micro-mirror in response to the logic state latched by the memory cell.

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