WO2024127394A1 - Étalon mems accordable à atténuation de dérive parasite - Google Patents

Étalon mems accordable à atténuation de dérive parasite Download PDF

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Publication number
WO2024127394A1
WO2024127394A1 PCT/IL2023/051260 IL2023051260W WO2024127394A1 WO 2024127394 A1 WO2024127394 A1 WO 2024127394A1 IL 2023051260 W IL2023051260 W IL 2023051260W WO 2024127394 A1 WO2024127394 A1 WO 2024127394A1
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WIPO (PCT)
Prior art keywords
filter
cap
frame structure
mirror
actuation
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PCT/IL2023/051260
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English (en)
Inventor
Eliahu Chaim ASHKENAZI
Stav Eitan RIGER
Viacheslav Krylov
Avraham MENDELSON
Yoed ABRAHAM
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Unispectral Ltd.
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Application filed by Unispectral Ltd. filed Critical Unispectral Ltd.
Publication of WO2024127394A1 publication Critical patent/WO2024127394A1/fr

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  • MEMS Micro-Electro-Mechanical systems
  • a tunable spectral filter such as an etalon (also known as a Fabry-Perot filter), consists of two parallel semi-transparent elements, such as mirrors, forming its core structure.
  • the gap between these mirrors also referred to as “optical gap” or “optical cavity” dictates the filter's spectral transmission profile, commonly referred to as the "filter-state.”
  • Some etalon designs feature a configuration with one movable mirror and one stationary mirror, while other designs incorporate two movable mirrors. By varying the voltage applied to multiple electrodes, the distance between the mirrors is altered, thus adjusting the optical gap, and tuning the etalon's spectral transmission properties.
  • MEMS Micro-Electro-Mechanical systems
  • a MEMS tunable filter comprising a first mirror and a second mirror having a tunable gap deposited therebetween, a frame structure coupled to the first mirror, and electrodes; the filter further comprising or is otherwise operatively connected to a control and processing circuitry configured to control actuation of the electrodes to obtain a plurality of filter states, each filter state corresponding to a respective gap that is characterized by a respective transmission profile; the MEMS tunable filter comprises at least one structural element (e.g., stopper) that accumulates, during actuation of the electrodes, parasitic charge thereon; wherein the control and processing circuitry is configured, responsive to determination that a condition is met, to execute a drift reset procedure, comprising: actuating the electrodes such that the frame structure is moved, causing at least one electrode to touch
  • a drift reset procedure comprising: actuating the electrodes such that the frame structure is moved, causing at least one electrode to touch
  • the MEMS tunable filter according to this aspect of the presently disclosed subject matter can optionally comprise one or more of features (i) to (xv) below, in any technically possible combination or permutation.
  • the first mirror is fixed to the frame structure on one side and wherein a cap is located on another side of the frame structure; wherein the structural element is a stopper that is fixed to the cap and separates between the cap and the frame structure, and wherein, during actuation, as part of the drift reset procedure, the frame structure is moved towards the cap so at least one electrode that is fixed to the frame or is integrated in the frame touches the stopper.
  • the cap is located at an object side relative to the first mirror.
  • the cap comprises a conductive material covered area on which conductive material is deposited, and wherein there are gaps on the cap devoid of conductive material between the conductive material covered areas and the stopper; wherein the at least one electrode is fixed to the frame or integrated in the frame and the conductive material covered areas are positively charged; and wherein the size of the gaps is such that positive charge can leak from the positively charged conductive material covered area to the stopper accumulating as parasitic charge on the stopper.
  • a conductive material is deposited on the cap to obtain conductive material covered areas, and wherein there are gaps on the cap devoid of conductive material between the conductive material covered areas and the stopper; wherein the frame structure is positively charged and wherein the conductive material covered areas are negatively charged; and wherein the size of the gaps is such that negative charge leaks from the negatively charged conductive material covered area to the stopper.
  • the MEMS etalon filter further comprises or is otherwise operatively connected to one or more lenses.
  • the MEMS etalon filter further comprises or is otherwise operatively connected to an image sensor configured to capture at least one image in each filter state to thereby obtain a plurality of respective images.
  • the frame structure is made of silicon. viii.
  • At least one actuation electrode is integrated in the frame structure.
  • the frame structure is implemented as an actuating electrode.
  • the condition is a predefined period and wherein the control and processing circuitry is configured to execute the drift reset procedure once the predefined period has passed.
  • the MEMS etalon filter further comprises or is otherwise operatively connected to a sensor configured to capture at least one image in each filter state to thereby obtain a plurality of respective images; wherein the condition includes detection of one or more image degradation parameters, wherein the control and processing circuitry is configured to apply, in real-time, image processing on the plurality of respective images, and execute the drift reset procedure responsive to detection of one or more image degradation parameters.
  • condition is a value of charge accumulating on the stopper, wherein the control and processing circuitry is configured to determine a value of charge accumulating on the stopper and execute the drift reset procedure once the value of charge is greater than a certain threshold.
  • condition is a capacitance value measured between the frame and the cap, wherein the control and processing circuitry is configured to obtain data indicative of the capacitance value and execute the drift reset procedure once the capacitance value is greater than a certain threshold.
  • condition is completion of a particular sequence of actuations, each actuation corresponding to a respective filter state calibrated while considering drift induced by the parasitic charge
  • control and processing circuitry is configured to execute the drift reset procedure following completion of actuation of the sequence of actuations.
  • control and processing circuitry is configured to execute a model that receives as input a sequence of actuations, each actuation corresponding to a respective filter state, and calculate an accumulative parasitic charge resulting from the sequence of actuations; the control and processing circuitry is configured to execute the drift reset procedure responsive to a model output indicating that the accumulative parasitic charge is greater than a predefined threshold value.
  • a method of augmenting operation of a MEMS tunable filter comprising: a first mirror and a second mirror having a tunable gap deposited therebetween, a frame structure coupled to the first mirror, and electrodes; the filter further comprising or is otherwise operatively connected to a control and processing circuitry configured to control actuation of the electrodes to obtain a plurality of filter states, each filter state corresponding to a respective gap that is characterized by a respective transmission profile; the MEMS tunable filter comprises at least one structural element (e.g., stopper) that accumulates, during actuation of the electrodes, parasitic charge thereon; the method comprising: controlling actuation of the electrodes to obtain a sequence of filter states, each filter state corresponding to a respective gap that is characterized by a respective transmission profile; responsive to determination that a certain condition is met, executing a drift reset procedure, comprising: actuating the electrodes such that the frame structure is moved, causing at
  • the presently disclosed subject matter further contemplates a non-transitory computer readable storage medium tangibly embodying a program of instructions that, when executed by a processing circuitry in a MEMs tunable filter, causes the filter to perform a method of discharging parasitic charge accumulated on an element (e.g., stopper) as described above with respect to the first and second aspects.
  • an element e.g., stopper
  • control and processing circuitry comprising at least one processor and non- transitory computer memory operatively connectible to or interoperable with a MEMS tunable filter, and configured, responsive to determination that a condition is met, to execute a drift reset procedure, comprising: actuating electrodes of the MEMS etalon filter such that a frame structure touches a structural element (e.g., stopper fixed to a cap) to thereby discharge a parasitic charge that has accumulated on the structural element.
  • a control and processing circuitry e.g., controller
  • a control and processing circuitry comprising at least one processor and non- transitory computer memory operatively connectible to or interoperable with a MEMS tunable filter, and configured, responsive to determination that a condition is met, to execute a drift reset procedure, comprising: actuating electrodes of the MEMS etalon filter such that a frame structure touches a structural element (e.g., stopper fixed to a cap) to thereby discharge a parasitic charge that has
  • the presently disclosed subject matter further contemplates a device comprising a MEMS etalon filter, a control and processing circuitry, and an image sensor;
  • the MEMS etalon filter comprising: a first mirror and a second mirror having a tunable gap deposited therebetween, a frame structure coupled to the first mirror, and actuation electrodes;
  • the control and processing circuitry is configured to control actuation of the electrodes to obtain a plurality of filter states, each filter state corresponding to a respective gap that is characterized by a respective transmission profile;
  • the image sensor is configured to capture at least one image in each filter state to thereby obtain a plurality of respective images;
  • the MEMS tunable filter comprises at least one structural element that accumulates, during actuation of the electrodes, parasitic charge thereon;
  • the control and processing circuitry is configured, responsive to determination that a condition is met, to execute a drift reset procedure, comprising: actuating the electrodes such that the frame structure is moved, causing at least one electrode
  • the method, the non-transitory computer readable storage medium, the processing circuitry and the device, disclosed herein, can optionally further comprise one or more of features (i) to (xv) listed above, mutatis mutandis, in any technically possible combination or permutation.
  • FIG. 1A shows schematically, in an isomeric view, a tunable MEMS etalon filter, according to an example of the presently disclosed subject matter
  • FIG. IB shows schematically the device of FIG. 1A with a cross section, according to an example of the presently disclosed subject matter
  • FIG. 2A shows the device of FIG. IB in un-actuated state, according to an example of the presently disclosed subject matter
  • FIG. 2B shows the device of FIG. 2A in an actuated state, according to an example of the presently disclosed subject matter
  • FIG. 2C shows the device of FIG. 2A in an actuated state pull-in, according to an example of the presently disclosed subject matter
  • FIG. 3 shows schematically a top view of the functional mechanical layer in the device of FIG. 1A or FIG. IB, according to an example of the presently disclosed subject matter;
  • FIG. 4 shows schematically a top view of the cap in the device of FIG. 1A or FIG. IB with multiple electrodes formed thereon, according to an example of the presently disclosed subject matter;
  • FIG. 5 shows, schematically, charges deposited on elements of the MEMs etalon filter, according to examples of the presently disclosed subject matter
  • FIG. 6 shows, schematically, accumulation of parasitic charges on stopper 122 of the MEMs etalon filter, according to examples of the presently disclosed subject matter
  • FIG. 7 shows, schematically, release of parasitic charges accumulated on stopper 122 of the MEMs etalon filter, according to examples of the presently disclosed subject matter
  • FIG. 8 is a block diagram schematically illustrating a device comprising a MEMS etalon filter according to examples of the presently disclosed subject matter.
  • FIG. 9 is a flowchart of operations performed for release of parasitic charges, according to examples of the presently disclosed subject matter.
  • control and processing circuitry should be expansively construed to include any kind of suitable hardware electronic device with a control and data processing circuitry (e.g., digital signal processor (DSP), a Graphics Processing Unit (GPU), a Tensor Processing Unit (TPU), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), microcontroller, microprocessor etc.), which can comprise, for example, one or more processors operatively connected to computer memory of any sort, loaded with executable instructions for executing operations as further described below.
  • DSP digital signal processor
  • GPU Graphics Processing Unit
  • TPU Tensor Processing Unit
  • FPGA field programmable gate array
  • ASIC application specific integrated circuit
  • microcontroller microprocessor etc.
  • FIGS. 1 to 8 provide detailed illustrations sselling various features and aspects of the etalon design. These figures are intended to demonstrate certain structural and functional features of the etalon to enhance understanding of the presently disclosed subject matter. However, it is important to note that these depictions should not be construed as limiting the scope of the etalon. They are merely representative examples, while the etalon may encompass a broader range of variations, modifications, and alternative configurations that fall within the scope of the underlying principles of the presently disclosed subject matter, as outlined in the description.
  • FIG. 1A shows schematically, in an isometric view, a first example of a tunable MEMS etalon device (or filter) disclosed herein and numbered 100.
  • FIG. IB shows an isometric cross section of device 100 along a plane marked A-A.
  • Device 100 is shown in conjunction with a XYZ coordinate system, which also holds for all following drawings.
  • FIGS. 2A, 2B and 2C show cross sections of device 100 in plane A-A in unactuated state (FIG. 2A), an actuated state (FIG. 2B) and actuated pull-in state (FIG. 2C).
  • Device 100 comprises two substantially flat and parallel mirrors (typically with partial reflective surfaces), a bottom (or “back”) mirror 102 and a top (or “aperture”) mirror 104 separated by an optical gap.
  • the terms “front” and “back” refer to the proximity of the mirror to the cap, where front mirror 104 is located closer to cap 118 and back mirror 102 is located further away from the cap 118.
  • the front (top) mirror is positioned nearer to the entry point where the light rays begin their path through the etalon, however this is not necessarily always the case.
  • the mirrors are formed in flat plates or wafers made of transparent or semi-transparent material, in a desired wavelength range transmitted by the tunable etalon filter (e.g., glass).
  • the degrees of reflectivity/transparency of the top and back mirrors are selected in accordance with the desired spectral transmission properties of the etalon.
  • each mirror is at least semi- reflective to some degree.
  • the term "plate”, “wafer” or “layer” refers to a substantially two-dimensional structure with a thickness defined by two parallel planes and having a width and a length substantially larger that the thickness. "Layer” may also refer to a much thinner structure (down to nanometers-thick, as opposed to a typical thickness of micrometers for the other layers).
  • back mirror 102 is formed in a glass layer that also serves as a substrate of the device.
  • back mirror 102 may be formed in a "hybrid" plate or hybrid material such that a central section ("aperture") through which the light rays pass is at least partially transparent to the wavelength of the light (made e.g., of a glass), while plate sections surrounding the aperture are made of a different material, for example silicon.
  • the hybrid aspect may increase the stiffness and strength of the mirror.
  • silicon is used herein as a general non-limiting example. It is noted that the term silicon should not be construed as limiting, and other materials are also contemplated, including any material or combination of materials with suitable flexibility and durability required for the flexure structure to function in a desired way, for example plastic or glass.
  • the mirrors are movable with respect to each other, so that the optical gap can be tuned between certain minimal (gMn) and maximal (gMx) gap sizes.
  • the movement is in the Z direction in the particular coordinate system shown.
  • back mirror 102 is fixed, and front mirror 104 is movable.
  • the other mirror may be movable, or both mirrors may be movable.
  • the maximal optical gap size gMx corresponds to a "maximal" actuated state. There are, of course, many actuated states (and even a continuous range of states) in which the optical gap has a value gi between gMn and gMx.
  • device 100 may further comprise a first stopper structure (also referred to as "back stoppers") 106 positioned between mirrors 102 and 104 in a way such as not to block light rays from reaching an image sensor.
  • Back stoppers 106 may be formed on either mirror. When the two mirrors are in close proximity to each other, the minimal gap distance g Mn is defined by back stoppers 106 which function as displacement limiters.
  • An additional function of back stoppers 106 is to prevent undesirable displacement of the front mirror due to external shock and vibration.
  • Back stoppers 106 are designed to prevent contact between the mirrors and ensure that gMn is never zero. They may be located within an optical aperture area if their size is small, and they do not significantly obscure the optical signal.
  • back stoppers 106 are made of a metal for example, a patterned Cr-Au layer, Ti-Au layer, or Ti-Pt layer.
  • device 100 further comprises a mounting frame structure (or simply “frame”) 108 with an opening (“aperture”) 110.
  • frame or “frame structure” should be broadly construed to include any suspension structure used for supporting the mirror.
  • Frame 108 is made of an opaque, transparent, or semitransparent material (for example single crystal silicon) and is fixedly attached (e.g., by bonding) to front mirror 104. That is, mirror 104 is “mounted” on frame 108 and therefore moves together with frame 108.
  • opening 110 allows light rays to enter the etalon through the front mirror. Therefore, the front mirror is also referred to in such cases as an "aperture mirror".
  • back mirror 102 and optionally front mirror 104 include a multilayer thin-film optical coating deposited on a glass layer/substrate.
  • a device disclosed herein may comprise one or more electrodes (not shown) formed on back mirror 102 on the surface facing frame 108, to enable actuation of the frame structure (and thereby cause movement of the front mirror) toward the back mirror.
  • device 100 further comprises an anchor structure (or “anchor layer” or simply “anchor”) 112, made of an opaque, a transparent, or semitransparent material (for example single crystal silicon).
  • Anchor 112 and frame 108 are attached to each other by a flexure/suspension structure.
  • the suspension structure may, for example, be a region of anchor structure 112 patterned in the form of a bending or torsional spring, a combination of such springs, or as a thin doughnutshaped membrane adapted to carry the front mirror.
  • the suspension structure includes a plurality of suspension springs/flexures.
  • the plurality of suspension springs/flexures includes four springs, 114a, 114b, 114C, and 114d, made of opaque, transparent, or semitransparent material (for example single crystal silicon). Together, frame 108, anchor 112, and springs 114, form a "functional mechanical layer" 300, shown in a top view in FIG. 3.
  • spacers 116 can be formed of a glass material. Spacers 116 are used to separate the frame and springs from the plate in which mirror 102 is formed. While, in principle, anchors 112 could be attached to the bottom plate directly without spacers 116, this may require very large deformation of the springs. To avoid this deformation of the spring material, spacer layers 116 are used. In some examples, for technological reasons, both movable front mirror 104 and spacers 116 are fabricated from the same glass plate (wafer). This simplifies fabrication since the glass and silicon wafers are bonded at wafer level.
  • Device 100 further comprises a cap plate (or simply "cap") 118 accommodating at least part of an actuation mechanism configured for controlling gap size between the front mirror and the back mirror.
  • cap 118 is located at the object side relative to front mirror 104 at the direction of incoming light. In other examples, the configuration may be reversed, where cap 118 is located at the sensor side, and back mirror 102 is located at the object side.
  • cap 118 accommodates electrodes 120 formed on or attached thereto (see FIGS. 12A to 12C). Electrodes 120 can be positioned for example at a bottom side (facing the mirrors) of cap 118. Electrodes 120 are in permanent electrical contact through one or more through-glass vias 124 with one or more bonding pads 126 positioned on the opposite (top) side of cap 118. Electrodes 120 are used for actuation of frame 108 (thereby causing movement of front mirror 104).
  • the cap comprises a first recess (cavity) 119 to provide an actuation gap d between frame 108 and electrodes 120 (otherwise referred to as an "electrostatic gap"). As shown below with reference to FIGS. 5-7, other designs for creating the actuation gap can be used.
  • Device 100 further comprises front stoppers 122 that separate between frame 108 and cap 118.
  • front stoppers 122 isolate electrically (prevent electrical shorts between) frame 108 from cap electrodes 120.
  • front stoppers 122 define a maximal gap between front mirror 104 and back mirror 102.
  • the cap is made of a glass material.
  • cap 118 may be made of a "hybrid" plate or hybrid material, such that a central section ("aperture") through which the light rays pass, is at least partially transparent to the wavelength of the light (made e.g., of glass), while plate sections surrounding the aperture are made of a different material, for example silicon.
  • the hybrid aspect may increase the stiffness and strength of the cap.
  • the length L and width W (FIG. 1A) of mirrors 102 and 104 should, on the one hand, be large enough (e.g., in the order of several hundred micrometers ( A m) to several millimeters (mm)) to allow light passage to a relatively wide multi-pixel image sensor.
  • the minimal gap g Mn should be small enough (e.g., a few tens of nanometers (nm)) to allow desired spectral transmission properties of the etalon.
  • g Mn may have a value of down to 20 nanometers (nm), while gMx may have a value of up to 2 microns (urn). According to one example, the value of gMx may be between 300 to 400 nm. Specific values depend on the required optical wavelength and are dictated by a specific application. Thus, in some examples, gMx may be greater than gMn by one to two orders of magnitude.
  • back mirror 102 includes a second recess 128 with a depth t designed to provide pre-stress of the springs after assembly/bonding.
  • recess depth t is chosen on the one hand, such that the contact force arising due to deformation of the springs and the attachment of front movable mirror 104 to back stoppers 106 is high enough to preserve the contact in the case of shocks and vibrations during normal handling of the device.
  • the combined value of recess depth t plus the maximal required travel distance (maximal optical gap size) gMx is smaller than one third of an as-fabricated ("electrostatic") gap size do of a gap between electrodes 120 and frame 108 (i.e., a minimal gap between electrode 120 and frame 108 present at an "as fabricated state" following fabrication of the device), to provide stable controllable electrostatic operation of the frame by the electrodes located on the cap.
  • the as-fabricated electrostatic gap do may have a value of about 2-4 urn and t may have a value of about 0.5-1 urn.
  • the requirement for stable operation is t + g Mx ⁇ d 0 /3, since the stable travel distance of a capacitive actuator is 1/3 of the as-fabricated electrostatic gap, i.e., is d 0 /3.
  • FIGS. 2A and 2B show circuitry 130 configured for applying voltage on the electrodes for tuning the optical gap between the mirrors.
  • device 100 is fully transparent. It includes a transparent back mirror (102), a transparent front mirror (104), and a transparent cap (118), as well as transparent functional mechanical layer 300.
  • a transparent back mirror 102
  • a transparent front mirror 104
  • a transparent cap 118
  • transparent functional mechanical layer 300 One advantage of the full transparency is that the device can be observed optically from two sides. Another advantage is that this architecture may be useful for many other optical devices incorporating movable mechanical/optical elements, such as mirrors, diffractive gratings, or lenses.
  • device 100 is configured as a full glass structure, where the functional mechanical layer includes a glass substrate that is patterned to accommodate/define the suspension structure carrying the top mirror, the suspension structure including a plurality of glass springs/flexures.
  • FIG. 3 shows schematically a top view of functional mechanical layer 300.
  • the figure also shows an external contour 302 of front mirror 104, aperture 110, anchor structure 112, springs 114a-d (flexure structure) and a contour 304 enclosing a eutectic bond frame 121.
  • FIG. 4 shows schematically a top view of cap 118 with a plurality of electrodes 120, marked here 120a, 120b, 120c and 120d.
  • the number and shape of electrodes 120 are shown by way of example only and should not be construed as limiting. According to some examples, three electrodes 120 are required to control both the displacement of the frame in the Z direction and the tilting of the frame about X and Y axes. Multiple electrode regions, e.g., as shown in FIG.
  • cap 118 may be fabricated on cap 118 such that front mirror 104 can be actuated with an up-down degree of freedom (DOF) along the Z direction and can also be tilted (e.g., with respect to two axes X and Y) to provide additional angular DOF(s). This allows adjustment of angular alignment between front mirror 104 and back mirror 102.
  • DOF up-down degree of freedom
  • cap 118 may include a deposited eutectic bonding material 121.
  • cap 118 is made of glass (or glass like material) and a layer of Titanium Tungsten (TiW) is deposited on the internal side of the cap facing towards the mirror.
  • TiW Titanium Tungsten
  • a conductive material such as gold or silver, is deposited on the external and internal surface of cap 118 electrically connected with via (132) passing through the cap (e.g., through glass via, e.g., made of Tungsten).
  • the conductive material forms part of the actuation circuitry 130 for tuning the optical gap.
  • Tiw is used as a kind of intermediary material to avoid placing the conductive material directly on the glass cap, as it improves adhesion of the gold to the glass.
  • cap 118 of the MEMEs etalon device shown in FIGS. 2A-2C which has a curved internal structure that bends towards anchors 112 and creates cavity 119
  • cap 118 of the MEMEs etalon device shown in FIGS. 5, 6, and 7 has a substantially straight structure.
  • eutectic bonding material 121 is used for supporting cap 118 and holding it against the frame.
  • spacers 111 can be added to further support the cap over the frame, as shown in FIG 5.
  • the conductive material plating As illustrated, there are small gaps (indicated by arrows) between the conductive material plating and the stopper 122, which is made of a metallic material such as nickel.
  • the conductive material plating e.g., gold plating
  • negative charges are accumulated on the functional mechanical layer (including, frame 108, anchor 112 and springs 114).
  • FIG. 6 shows the parasitic-induced state.
  • parasitic charges As shown in FIG. 6, due to the miniscule dimensions of the gaps (e.g., at the order of 10 urn) between the gold plating and the stopper 122 and the conductively of the stopper 122, over time (Ti>To), positive charges leak from the conductive material to the stopper and accumulate on the stopper 122 (referred to herein as "parasitic charges” or “drift”).
  • the parasitic charges increase the pull power between the mirrors, such that for a given voltage applied by the electrodes, the resulting gap is different to the gap which is obtained by the same voltage in the nominal, parasitic-free state.
  • the accumulation of parasitic charges increases over time up to a certain maximal value.
  • the parasitic charges result in inaccurate actuation and an unstable filter state, leading to degraded performance of the MEMS etalon.
  • the presently disclosed subject matter includes a method and system configured to mitigate the parasitic charges and avoid the degradation in accuracy caused by these charges.
  • the cap is negatively charged, and the frame structure is positively charged.
  • the drift reset procedure as disclosed herein for mitigating parasitic charges can be likewise applied in such cases.
  • the MEMS etalon comprises or is other operatively connected to a control and processing circuitry configured to execute a drift reset procedure.
  • the drift reset procedure includes applying voltage for actuating the device (e.g., the frame structure 108) and thereby causing movement of the frame 108 such that it touches (is in physical contact with) stoppers 122.
  • FIG 2C demonstrates a "drift reset" operation where the frame 108 is pressed towards the stoppers 122.
  • FIG. 7 shows a drift reset operation in more detail demonstrating the transition of the negative charges from functional mechanical layer 300 (e.g., frame 108) to the stopper, thereby 'short circuiting' and discharging parasitic charge from the stopper 122.
  • control and processing circuitry can be configured to repeatedly execute the drift reset procedure in order to repeatedly reset the accumulating charge on the stopper. This operation can be performed quickly and for a very short while, so as to avoid interruption to the normal operation of the device.
  • FIG. 8 is a schematic block diagram showing an example of a device comprising the MEMs etalon filter disclosed herein.
  • FIG. 8 shows device 80 comprising device housing dedicated for holding together and protecting the device components.
  • Device 80 comprises from object side to sensor side, one or more filters 81, MEMs etalon filter 83, optical elements 85 and image sensor 87.
  • Filters 81 can include for example a bandpass filter designed to selectively allow light of a specific wavelength to enter the filter.
  • Device 80 further includes circuitry 130 configured for applying voltage on the electrodes for tuning the optical gap between the mirrors and control and processing circuitry 89.
  • Control and processing circuitry 89 is configured in general to control the operation of the etalon device 80.
  • Control and processing circuitry 89 is operatively coupled to circuit 130 for applying voltage and controlling actuation of electrodes to obtain a sequence of filter states, each filter state corresponding to a respective optical gap that is characterized by a respective transmission profile.
  • Control and processing circuitry 89 comprises one or more processors configured to execute various operations.
  • the control and processing circuitry can be configured to use the processors for executing several functional modules in accordance with computer-readable instructions implemented on a non-transitory computer-readable storage medium.
  • Such functional modules are referred to hereinafter as comprised in the processing circuitry.
  • FIG. 9 is a flowchart of operations executed for resetting parasitic charge, according to examples of the presently disclosed subject matter. By way of example only, certain operations in FIG. 9 are described with reference to components in device
  • the MEMS etalon filter 83 is controlled for actuating the electrodes, one or more times, each time adapting the optical gap to obtain a desired transmission profile.
  • control and processing circuitry 89 can be configured for creating/capturing colored image data by sequentially operating tunable MEMS etalon device for sequentially filtering light incident thereon for example, with three or more filter-states, each filter state corresponding to a different optical gap providing a different spectral filtering curves/profiles, and operating the sensor for acquiring images (monochromatic images/frames) of the light filtered by the three or more spectral curves respectively.
  • the control and processing circuitry is configured to actuate the optical gap of the MEMs etalon filter 83 to thereby maintain each of the filter states for corresponding time slot durations, during which a sensor is operated for capturing the respective monochrome images with respective integration times fitting in these time slots. Accordingly, each of the captured monochrome images corresponds to light filtered by a different respective spectral filtering curve and captured by a sensor over a predetermined integration time.
  • the MEMS etalon filter is used for switching between two or more bands.
  • these could be two near infra-red (NIR) bands, where the MEMS etalon filter is used instead of using two NIR filters design, where each filter has a different non-tunable bandpass capability.
  • Control and processing circuitry 89 can be configured for tuning the filter between two filter-states, one corresponding to a first band, and the other corresponding to a second band.
  • control and processing circuitry 89 is operatively connected to circuit 130.
  • instructions to capture a sequence of monochromatic images, or instructions to switch between bandpass states can be received in input buffer 891, e.g., by a user interacting with the device, or by way of upload from another computer device.
  • etalon actuator 893 controls actuation of the etalon filter 83 by controlling the voltage and time duration applied by circuit 130 on electrodes 120.
  • control and processing circuitry can be further configured to receive and process readout data (e.g., by image processing module 897) indicative of the three or more monochrome images from the sensor, and generate data indicative of a colored image (namely an image including information on the intensities of at least three colors in each pixel of the image).
  • a colored image namely an image including information on the intensities of at least three colors in each pixel of the image.
  • each image represents a narrow wavelength range of the electromagnetic spectrum, also known as a spectral band.
  • control and processing circuitry 89 is configured to determine (e.g., as the images are being captured) whether a certain condition is met, and if so, to execute a drift rest procedure.
  • reset monitor 893 can be configured to track adherence to one or more predefined conditions. In case it is determined that that these conditions are met, reset monitor 893 is configured to generate a command to initiate the drift reset procedure and provide the command to etalon actuator 895.
  • Examples of conditions that can be used for the activation of the drift reset procedure include:
  • Time dependent actuation - executing the drift reset procedure every period, e.g., every 5 seconds.
  • Image processing - applying real-time image processing on the output images and executing the drift reset procedure if one or more image degradation parameters are identified. For example, if gradual degradation in brightness of the sequence of images (or in a particular part of the image) which complies with some criterion is identified, instructions to execute the drift reset procedure are generated.
  • reset monitor 893 can be configured to apply image processing on images received from the image processing module 897.
  • Capacitance drift monitoring - applying real-time capacitance measurements between the electrodes in the frame 108 and cap 118.
  • Processing and control circuitry 89 can be configured, for example, to activate the drift reset procedure once the change in capacitance is greater than a certain threshold.
  • a dedicated circuit can be added to the etalon, e.g., integrated on the same wires used for actuating the optical gap (not shown).
  • Pre-calibrated activation sequence - charge accumulation during one or more specific sequences of actuations is pre-calibrated (while considering accumulation of parasitic charge) and stored on a computer memory (e.g., operatively connected to reset monitor 893).
  • a computer memory e.g., operatively connected to reset monitor 893.
  • the time points where excess charge accumulates on the stopper is determined in the lab.
  • the drift reset procedure can be executed according to the known time points.
  • a lookup table can be generated, storing one or more records, each record corresponding to a particular actuation sequence (each actuation sequence corresponding to a desired imaging output), and one or more respective time points for execution of the drift reset procedure along the sequence. When a certain actuation sequence is being executed, the lookup table is queried, and drift reset is executed accordingly.
  • laboratory calibration includes capturing the sequence of images, where, for each image, a respective filter-state is applied, and the respective transmission curve is measured. This would provide the correct wavelength range in each filter-state resulting from the nominal (desired) gap and the effect of the drift induced by the parasitic charge. Given this information, corrected actuation, that cancels the drift induced error, can be determined. Once the etalon device is calibrated according to the parasitic charge, the same specific sequence of images can be captured, and, after each time the specific sequence of images are captured, a drift rest is executed.
  • the control and processing circuitry is configured to execute a model that receives, as input, a sequence of actuations, each actuation corresponding to a respective filter state, and calculate, based on the voltage and time of actuation of each actuation in the sequence, an accumulative parasitic charge resulting from the sequence of actuations.
  • the control and processing circuitry is configured to execute the drift reset procedure responsive to determining that the accumulative parasitic charge is greater than a predefined threshold value.
  • the model can be implemented as a logic-based model, based on laboratory experiments.
  • the model can be implemented as a machine learning model, trained based on multiple different actuation sequences, for example, a supervised machine learning model classifier dedicated for determining whether a certain actuation sequence, received as input, induces a parasitic charge on the stopper which should be neutralized by the drift reset procedure.
  • reset monitor 893 is configured to receive as input an actuation sequence, execute the model, and determine, according to the model output, whether and when to execute the drift reset procedure.
  • more than one condition can be used. For example, activation of the drift reset procedure can be initiated if either a prescribed time has passed, or a certain capacitance value has been identified.
  • the drift reset procedure comprises applying volage on the electrodes to actuate the gap, such that at least one electrode touches the stopper 122 (block 95).
  • the frame needs to touch the stopper; in other cases, where the electrode is otherwise fixed to the frame structure, the frame is moved such that the electrode touches the stopper.
  • drift reset procedure Following execution of a drift reset procedure, it is repeated and executed again if the relevant condition(s) is met again.
  • the MEMS device comprises a control and processing circuitry configured, responsive to determination that a certain condition is met, to execute a drift reset procedure, comprising actuating the electrode such that the moving electrode and/or frame touches the element

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Abstract

La présente divulgation comprend un filtre accordable MEMS ayant une capacité d'atténuation de charge parasite. Un circuit connecté de manière fonctionnelle au filtre accordable MEMS est configuré, en réponse à la détermination du fait qu'une condition est satisfaite, pour exécuter une procédure de réinitialisation de dérive, comprenant des électrodes d'actionnement du filtre étalon MEMS, de telle sorte qu'une structure de cadre touche un élément structural (par exemple, une butée fixée à un capuchon) pour ainsi décharger une charge parasite qui s'est accumulée sur l'élément structural.
PCT/IL2023/051260 2022-12-11 2023-12-11 Étalon mems accordable à atténuation de dérive parasite WO2024127394A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6707593B2 (en) * 2001-05-08 2004-03-16 Axsun Technologies, Inc. System and process for actuation voltage discharge to prevent stiction attachment in MEMS device
US6836366B1 (en) * 2000-03-03 2004-12-28 Axsun Technologies, Inc. Integrated tunable fabry-perot filter and method of making same
US20090057792A1 (en) * 2004-12-22 2009-03-05 Koninklijke Philips Electronics N.V. Charge biased mem resonator
US20130314794A1 (en) * 2012-05-25 2013-11-28 Axsun Technologies, Inc. Tunable Filter with Levered Membrane and Longer Scan Length

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6836366B1 (en) * 2000-03-03 2004-12-28 Axsun Technologies, Inc. Integrated tunable fabry-perot filter and method of making same
US6707593B2 (en) * 2001-05-08 2004-03-16 Axsun Technologies, Inc. System and process for actuation voltage discharge to prevent stiction attachment in MEMS device
US20090057792A1 (en) * 2004-12-22 2009-03-05 Koninklijke Philips Electronics N.V. Charge biased mem resonator
US20130314794A1 (en) * 2012-05-25 2013-11-28 Axsun Technologies, Inc. Tunable Filter with Levered Membrane and Longer Scan Length

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