Thin film actuation

Abstract

A system includes a thin-film actuator anchored to a motive panel. The motive panel is anchored to a second actuator, which may operate to selectively position an axis of motion of the thin-film actuator via motion of the motive panel relative to a base substrate to which the second actuator is anchored.

Description

THIN FILM ACTUATIONSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with government support under 2054148 awarded by the National Science Foundation and D18AP00071 awarded by the U.S. Department of Defense, Defense Advanced Research Projects Agency. The government has certain rights in the invention.PRIORITY

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 626,663, filed January 30, 2024, and titled Thin Film Actuation.BACKGROUNDTechnical Field

[0003] The disclosure relates generally to actuation in thin film systems.Brief Description of Related Technology

[0004] Micro-electromechanical systems (MEMS) have experienced rapid growth in development and adoption. However, MEMS, due to their small spatial dimensions, may have reduced functionality and flexibility compared to macroscale systems. Nevertheless, the small spatial footprint of MEMS has led to their adoption in a variety of applications, including display technologies, despite the challenges presented in maintaining their small size while providingfunctionality. Increases in functionality and flexibility of MEMS will continue to drive adoption of and demand for MEMS.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 shows an example out-of-plane thin-film actuation (OTFA) system.

[0006] Figure 2 shows an example method for operation of the OTFA system of Figure 1.

[0007] Figure 3 shows an illustrative example piezoelectric transducer based OTFA device.

[0008] Figure 4 shows an illustrative example method of fabrication for the illustrative example piezoelectric transducer based OTFA device of Figure 3.

[0009] Figure 5 shows an example method for OTFA-system-based sensing.DETAILED DESCRIPTION

[0010] Thin film actuators may be used to induce motion in various Micro-electromechanical system (MEMS) contexts. A thin-film actuator, such as a piezoelectric transducer, coupled to an electrode (e.g., for actuator driving) may be used to move various parts of a MEMS system generating in-plane “side-to-side” motion and / or “up-and-down” motion normal to the top surface of the device.

[0011] According to the conventional wisdom, the thin-film actuator must be rigidly anchored to the substrate so as to couple reliably to the electrode for stable contact with driving signal inputs. Moreover, according to the conventional wisdom, the rigid anchor to the substrate provides device robustness, which is desirable for MEMS components, which, in some cases, cannot be replaced or fixed within a larger device. Thus, MEMS component failure may lead to overall device performance degradation and / or failure.

[0012] Although not recognized by the conventional wisdom, out-of-plane motion, e.g., motion first reliant on the re-orientation of the thin-film actuator for micro-origami systems, by a second actuator is impracticable because such motion may be reliant on the thin-film actuator being non-rigidly coupled to the base substrate of the MEMS device. Thus, the techniques and architectures discussed herein are contrary to the conventional wisdom because the techniques and architectures rely on a motive panel with a first thin-film actuator anchored thereon. The motive panel movable via motion of a second actuator. Thus, in somecases, the thin-film actuator may be repositioned via non-rigidly coupled movement relative to a base substrate, to which the second actuator may be coupled.

[0013] Although not recognized by the conventional wisdom, mixed-transducer microorigami systems may allow for tailored MEMS folding operations. Piezoelectric devices may have a comparatively large folding radius (e.g., radius of the bend created when the actuator folds) relative to certain other actuator technologies. For example, some strained-morph actuator technologies, such as those discussed herein, may have relatively smaller folding radii. Nevertheless, thin film piezoelectric actuators may have other comparative advantages. Thus, a mixed-transducer micro-origami system may outperform a similar single transducer micro-origami system because the selection of individual transducers may be based on the specific comparative advantages of the selected transducer. Conventional systems may rely on uniformity within their selected transducers due to the conventional wisdom which holds that different types of transducers such as current-driven vs voltage-driven (or other differences), may lead to interference, e.g., mechanical interference and / or driving signal interference.

[0014] Figure 1 shows an example out-of-plane thin-film actuation (OTFA) system 100. In the example OTFA system 100, a thin-film actuator 110 may be anchored to a motive panel 120. The motive panel 120 may be coupled to a base substrate 130 (at least in part) by a second actuator 140. The second actuator 140 may include another thin-film actuator.

[0015] In various implementations, the thin-film actuator 110 and the second actuator 140 may include piezoelectric transducer, strained-morph actuators (or other multiple-material expansion-strain based actuators), and / or other actuator types. In various implementations, the thin-film actuator 110 and the second actuator 140 may be driven using the same driving signals, e.g., both driven using voltage signals, current signals, or other signal types.

[0016] In various illustrative examples, the thin-film actuator 110 may include a piezoelectric transducer and the second actuator 140 may include a strained-morph actuator, such as a bimaterial polymer-metal actuator. Accordingly, in these implementations, the thin-film actuator 110 may include a voltage-driven actuator, which may have its position controlled via application of a particular voltage level to the actuator, while the second actuator 140 may include thermally-driven actuator, may have its position controlled via by holding the material of the second actuator 140 at a particular temperature. Temperature of the second actuator140 may be selected through application of a particular current level through the actuator material. Accordingly, the actuator may, in some cases, be a current-driven actuator.

[0017] In an illustrative example, the second actuator 140 may include a bi-material polymer- metal actuator including a polymer layer (e.g., such as a SU-8 polymer) and a metal layer (such as gold, or other noble metal). As the temperature of the second actuator 140 is changed (e.g., via resistive heating due to a current signal though the metal layer), force from thermal expansion (including the difference in thermal expansion between the polymer and metal electrode) may overwhelm the contraction stress allowing the actuator to move into an unbent position. Allowing the temperature to be reduced (e.g., by removing the resistive heating) may cause the residual stress in the polymer to contract the polymer causing the bi-material film to bend once more. Accordingly, the second actuator 140 may bend due to the induced strain from residual stress in the polymer that may be selectively bent and relaxed via controlled heating.

[0018] The thin-film actuator 110 and the second actuator 140 may be coupled to electrodes 1 12, 142 and may provide driving signals to the actuators 110, 140. The electrodes may include metal layers, e.g., thin-film metal layers, including metals such as gold and / or other noble metals. In some implementations, the electrodes may be applied via sputter coating (and / or other deposition technique) followed by a pattern removal.

[0019] In the example OTFA system 100, the motive panel 120 is shown cantilevered via an edge of the motive panel being coupled (e.g., via anchor 144) to the second actuator 140. The second actuator 140 is then coupled, via anchor 146, on another end to the base substrate 130. The thin-film actuator 110 is coupled, via anchor 1 14 to the motive panel 120. The thin- film actuator may be configured to application panel 150, which may include an applicationspecific object 152 (e.g., an object to be positioned via the OTFA system 100), which may be positioned across multiple planes via the complex coordinated positioning provided via thin- film actuator 1 10 and the second actuator 140.

[0020] The cantilevered configuration of the motive substrate 120 allows for position of the motive substate 120 by the second actuator 140 as a movable flap with a selectable angle deflection from the base substrate 130.

[0021] The motive substrate 120 may be flexibly coupled to the base substrate via the second actuator 140 and / or flexible electrodes 1 12 for the thin-film actuator 1 10, without additional points of connection to the base substrate. Accordingly, the motive substrate 120and the thin-film actuator 140 may form a free-floating thin-film stack that may be position able via motion of the second actuator 140.

[0022] Although not shown, the motive substrate 120 may be coupled to the second actuator 140 at non-edge positions. For example, the second actuator 140 may couple to the underside face of the motive substrate 120 to create a “seesaw” type angle-deflection axis about which the motive substrate 120 may rotate. Other configurations are possible.

[0023] The electrodes 1 12 for the thin-film actuator 1 10 may include flexible electrodes such that the electrodes 1 12 may couple to contacts 1 1 1 disposed on the base substrate while maintaining electrical contact with the thin-film actuator 1 10. For example, the flexible electrodes may include deformable metal thin films (e.g., such as gold films and / or other noble metal films) that may bend (or otherwise deformed without breaking) as the anchor for the thin-film actuator 110 is repositioned via operation of the OTFA system 100. In some cases, spring coils and / or other flexible structures may be formed within the electrodes 112 to promote electrode flexibility. In some cases, the electrodes 112 may include materials similar to those that makeup the second actuator 140. For example, the second actuator 140 may include a bi-material polymer-metal actuator while the electrode 1 12 includes a metal layer encapsulated within a polymer layer for isolation. In some cases, the polymer layer that encapsulates the electrode may layer residual strain, e.g. such that the electrode does not contribute to actuation of the motive substrate 120 when exposed to signals for control of the thin-film actuator 110.

[0024] The OTFA system 100 may be sized to meet various application requirements. For example, the OTFA system 100 may be less than 3mm across the system’s largest dimension. For example, the OTFA system 100 may be less than 1 mm across the system’s largest dimension. In various example, the OTFA system may include as small as micron scale features and / or smaller features.

[0025] In some implementations, various layers of the OTFA system 100 may include polymer encapsulation layers and / or photoresist layers. Polymer encapsulation layers and / or photoresist layers may operate to electrically isolate various components of the OTFA system and may increase device robustness. Additionally or alternatively, polymer curing may be used to create different properties of different potions of the OTFA system 100. For example, rigid “hard-baking” may be used to form rigid motive panels, anchors, and / or other rigid features. Flexible curing may be used for encapsulated components that undergo bending, such aselectrode portions. As discussed above, residual stress may be used to implement motive force for actuation.

[0026] Figure 2 shows an example method 200 for operation of the OTFA system 100. A signal source, e.g., such as a voltage source and / or a current source in electrical contact with the electrodes 1 12, 142 may be activated (202). The activated signal source may provide a first signal of a selected level to selectively position the thin-film actuator 1 10 (204). The activated signal source may provide a second signal at another selected level to selectively position the second actuator (206). The first and second signals may be independently selected.

[0027] In various implementations, an OTFA system may be used for object handling. For example, the motive panel and / or application panel of the OTFA system may be positioned via the actuators to perform gripping actions and / or other object handling motions. In some cases, the object handling may include MEMS-scale small object handling.

[0028] Figure 5 shows an example method 500 for OTFA-system-based sensing. The application panel of an OTFA system is placed in contact and / or near-contact with a target surface (502). In some cases, the application panel may be coupled to a strained-morph actuator. The folding angle of the strained-morph actuator may be set as a result of pressure from contact with the target surface (504). The resistivity of the strained-morph actuator may be set via the resultant folding angle because the folding angle may determine the length of the thin-metal layer of the strained-morph actuator (506). The folding angle may be determined by measuring the resistivity of the strained-morph actuator (508). Thus, the strained-morph actuator of the OTFA system may behave as a stain gauge in addition to or in lieu of actuation behavior.

[0029] In some cases, the OTFA system may be a single gauge and / or single actuator system. For example, only a stained-morph gauge / actuator may be presented within the OTFA system.

[0030] In some cases, a second (or other multiple-actuator configuration) may be present in the OTFA system. In some cases, the strained morph actuator may be anchored to the motive panel of the OTFA system. Thus, fine-tuned positioning of the position sensing actuator may be achieved via actuation of the second actuator of the OTFA system. In some cases, the OTFA system may be a mixed-transducer system, e.g., where the position sensing actuator and at least one other actuator in the system differ in type. For example, a strained-morph actuator may be used as a strain-gauge for bend-angle sensing, while the OTFA system further includes a piezoelectric transducer (e.g., for fine-tuned positing of the strained-morphactuator via motion of a motive panel. The various actuators may be isolated from one another to avoid driving and / or detection signal interference.

[0031] In some cases, different actuators may have different functions. For example, a straingauge actuator may be used for vibration detection, while another actuator in the system may be used for vibration excitation. As an illustrative example, an OTFA system may include a stained-morph gauge that detects vibrations in a surface excited by the motion of the piezoelectric transducer of the OTFA system.

[0032] Example Implementations

[0033] Various illustrative example implementations are included herein. The illustrative example implementations are illustrative of the general architectures and techniques described above and in the claims below. The various individual features described with respect to the individual example implementations may be readily and optionally integrated with other implementations with or without various other features present in the respective example implementation.

[0034] Figure 3 shows an illustrative example piezoelectric transducer (PZT) based OTFA device 300. The illustrative example PZT-OTFA device 300, includes a PZT stack 310, a base silicon substrate 320, a polymer encapsulation layer 330, contact pads for electrodes 340, and a strained-morph actuator 350. The PZT stack 310 has four material layers including: a top platinum (Pt) electrode (0.15 pm) 312, a PZT (1 pm) 314, a bottom platinum electrode (0.15 pm) 316, and silicon dioxide (0.5 pm) 318. In the illustrative example PZT-OTFA 300, the PZT layer 314 is an active layer and the silicon dioxide layer 318 is a passive layer. When applying voltage across the top and bottom platinum electrodes, the thin-film PZT will contract and cause the strained-morph actuator 350 to bend upward. The strained-morph actuator 350 includes two layers of material: SU-8 (0.8 pm) and gold (0.2 pm). This strained-morph actuator 350 has two forms of actuation. Upward folding motion may be created using residual stresses stored within the SU-8 layer during fabrication. Heat treating the SU-8 film before release generates residual stress within the film, which will force the SU-8 to contract upon release. Thus, the force to support the upward bending motion is created. In the strained-morph actuator 350, downward folding motion is created by heating the bi-material morph after releasing the devices. In the strained-morph actuator 350, the gold layer may be patterned as an electro-thermal heater. When applying current through the gold layer, Joule heatingelevates the temperature of the bi-material morph. Because the SU-8 layer has a larger thermal expansion coefficient than the gold layer, downward folding occurs.

[0035] Because the PZT stack (including a rigid motive panel) is stiffer than the electrothermal actuators, the PZT stack may be made to be “free-floating” during fabrication, e.g., the PZT stack may not necessarily be anchored to the silicon dioxide substrate. Because of this “free-floating” design, combining the PZT actuator and the electro-thermal actuator may rely on the establishment of robust electrodes for the PZT stack. In the example PZT-OTFA 300, the PZT actuator stacks are setback between the top Pt, middle PZT, and bottom Pt layers. In some cases, the setback may reduce the occurrences PZT film shorting. In some implementations, a setback of 5 pm or more may be used, dependent on device geometry. A thin-film (0.8 pm) of SU-8 polymer may be used to encapsulate the PZT stack. The polymer may provide robustness and / or isolation for the PZT film during fabrication and / or operation of the PZT-OTFA 300.

[0036] In various implementations, a thin film of gold (0.2 pm) may be sputtered onto the system and patterned to create the electrical connections. Encapsulating the PZT in polymer may allow simultaneous use of the thin-film SU-8 layer as the elastomer-based actuator system used to fold the thin-film PZT layer out-of-plane. The PZT and elastomer-based actuator system may be combined using rigid photoresist panels. These rigid photoresist panels may also be used as the structural components for various OTFA configurations.

[0037] Figure 4 shows an illustrative example method 400 of fabrication for the illustrative example PZT-OTFA 300. A pre-fabricated silicon (Si) wafer with a PZT stack may be used as a starting form (402). As one illustrative example, the PZT stack may include a top platinum electrode 0.15 pm, 52 / 48 PZT 1 pm, bottom platinum electrode 0.15 pm, titanium dioxide 0.04 pm, silicon dioxide 0.5 pm. Other PZT configurations may be used. The PZT stack layers may be patterned to remove material for form the PZT actuator, electrodes, dioxide layers (404). As an example, ion milling may be used to pattern the PZT and electrode layers, and glass etching may be used to pattern the silicon dioxide and titanium dioxide layers. Setbacks between the top platinum layer, the PZT layer, and the bottom Pt layer may be created to reduce and / or eliminate shorting in the top and bottom electrodes. In some cases, excess photoresist may be removed via O2plasma stripping.

[0038] After patterning the PZT material stack, a bottom gold (Au) layer for strained-morph actuator 350 may be deposited (406). This gold layer is patterned using a liftoff process. Afterpatterning the liftoff resist, 0.2 pm of gold with an adhesion layer of 0.02 pm chromium may be applied using an evaporator.

[0039] A thin layer (0.8 pm) of polymer (e.g., SU-8 or similar polymer) may be deposited on top of the wafer (408). The SU-8 covers the PZT stack completely (e.g., confining exposure to small portions of the top and bottom electrodes). Thus, a wet etch may be used to pattern the top gold layer without damaging the PZT layer. Heat shrinking the SU-8 film may create strained morphs to achieve passive self-assembly upon release. Moreover, the thin film SU-8 is the active layer strained morphs may support fabrication of the strained-morph actuator system 350.

[0040] The gold layer may then be patterned (410) to form the electrode for control of the strained-morph actuator system 350. A photoresist layer (5 pm) is deposited and patterned used to create panels that connect different actuator systems (412).

[0041] Where multiple PZT-OTFA devices are fabricated together or a PZT-OTFA device is otherwise fabricated within a larger-than-device wafer, the fabricated device may be cut (414) out of the wafer as an individual device for application.

[0042] The present disclosure has been described with reference to specific examples that are intended to be illustrative only and not to be limiting of the disclosure. Changes, additions and / or deletions may be made to the examples without departing from the spirit and scope of the disclosure. Table 1 shows various examples.

[0043] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

Claims

What is Claimed is:

1. A device including: a thin-film piezoelectric transducer at least partially disposed on a cantilevered panel; and a thermally-driven actuator rotationally coupled to the cantilevered panel to cause rotation an axis of motion of the thin-film piezoelectric transducer.

2. The device of claim 1 , where the device includes a micro-electromechanical system (MEMS).

3. The device of claim 1 , where a largest dimension of the cantilevered panel is less than three millimeters.

4. The device of claim 1 , where the cantilevered panel includes a flap actuated via motion of the thermally-driven actuator.

5. The device of claim 1 , where the thin-film piezoelectric transducer is set back from an edge of the cantilevered panel.

6. The device of claim 1 , where the cantilevered panel and thin-film piezoelectric transducer include a free-floating thin-film stack.

7. The device of claim 6, where the thin-film piezoelectric transducer is disposed within polymer layers within the free-floating thin-film stack.

8. The device of claim 1 , where the thermally-driven actuator includes a strained-morph polymer-metal actuator.

9. The device of claim 1 , further including: a first sputtered-metal electrode coupled to the thin-film piezoelectric transducer; and a second sputtered-metal electrode coupled to the thermally-driven actuator.

10. A device including: a base substrate; a thin-film transducer disposed on a motive panel; a first electrode coupled to the thin-film transducer to supply a transducer driving signal, the first electrode disposed on the motive panel; an actuator coupling the base substrate to the motive panel, the actuator repositionable via an actuator driving signal to cause motion of the motive panel relative to the base substrate, the actuator driving signal different from the transducer driving signal; a second electrode isolated from the first electrode, the second electrode coupled to the actuator to supply the actuator driving signal different from the transducer driving signal.11 . The device of claim 10, where the transducer driving signal includes a voltage signal and / or the actuator driving signal includes a current signal.

12. The device of claim 10, where the motive panel includes a cantilevered panel, the actuator coupling an edge of the cantilevered panel to base substrate.

13. The device of claim 10, where the motive panel includes an angle-deflection panel, the actuator coupling a rotation axis of the angle-deflection panel.

14. The device of claim 10, where the actuator includes a multi-material actuator, actuation within the multi-material actuator effected via residual stress stored in one or more materials within the multi-material actuator.

15. The device of claim 14, where the multi-material actuator includes a strained- morph polymer-metal actuator.

16. The device of claim 10, where the thin-film transducer includes a piezoelectric transducer.

17. A device including: a voltage-driven thin-film actuator anchored to a motive panel; and a current-driven actuator coupled to the motive panel to cause rotation of and / or translation of an axis of motion of the voltage-driven thin-film actuator via motion of the motive panel.

18. The device of claim 17, where the device includes a micro-electromechanical system (MEMS).

19. The device of claim 17, where a largest dimension of the motive panel is less than three millimeters.

20. The device of claim 17, where: the device further includes a base substrate; and the motive panel and voltage-driven thin-film transducer include a free-floating thin- film stack anchored to the base substrate via the current-driven actuator.

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