WO2019171295A2

WO2019171295A2 - Thin film-based readout circuitry for triboelectric touch sensors

Info

Publication number: WO2019171295A2
Application number: PCT/IB2019/051813
Authority: WO
Inventors: Gato TORRES SEVILLA; Muhammad Mustafa Hussain; Jesus Alfonso CARAVEO-FRESCAS; Pradipta K. NAYAK; Fahad ALSALEM; Abdulaziz H. ALDUBAYAN; Ramzi Salem AL-MAGHATHUWI
Original assignee: Sabic Global Technologies B.V.
Priority date: 2018-03-08
Filing date: 2019-03-06
Publication date: 2019-09-12
Also published as: WO2019171295A3

Abstract

An example circuit for reading data from a triboelectric sensor includes a triboelectric sensor and a sensing element electrically coupled to the triboelectric sensor and configured to output a signal in response to a change in voltage from the triboelectric sensor. The sensing element may include a first thin film transistor electrically coupled to the triboelectric sensor. The circuit may further include a load element electrically coupled to the sensing element and configured to supply a load to the sensing element. The triboelectric sensor, the sensing element, and the load element may be disposed on a flexible substrate.

Description

THIN FILM-BASED READOUT CIRCUITRY FOR TRIBOELECTRIC TOUCH

SENSORS

Technical Field

[0001] The disclosure generally relates to thin films, and more particularly to thin film devices comprising triboelectric sensors.

Background

[0002] Conventional readout circuits for triboelectric sensors use special laboratory equipment and conventional silicon-based complimentary metal -oxide-semiconductor (CMOS) electronics. However, these conventional readout circuits for triboelectric sensors require printed circuit boards and rigid integrated circuits that hinder the possibility of use of triboelectric sensors in several applications where mechanical flexibility is required such as: wearable electronics, implantable electronics, mobile patch-like applications, among others. The use of conventional electronics as readout circuits has yielded several different architectures and combinations to convert the analog sensor signal into digital signals.

[0003] Commonly, active matrices similar to the ones used in display technologies are used as sensor readout circuits. Such display technologies may include the following conventional circuit configuration: a single thin film transistor with column and row select connections in the source and gate electrodes of the transistor respectively, a pressure or touch sensor with one terminal connected to the drain electrode of the transistor, and a supply voltage connected to the second terminal of the sensor. However, this conventional circuit configuration can only be used for resistive and capacitive sensors since the transistor current is varied only due to a change in resistance or capacitance of the sensor. Also, the conventional circuit configuration cannot be applied to triboelectric sensors due to at least the following reasons. Triboelectric sensors may comprise a single bottom terminal that serves as a current collector. Because only a single bottom terminal is available, a supply voltage cannot be connected to the triboelectric sensor. Additionally, triboelectric sensors cannot produce sufficient current to energize and drive a single transistor. Triboelectric sensors produce a change in voltage instead of a change in resistance or capacitance.

[0004] Thus, there is a need for improved integration of triboelectric sensors into thin films. Summary

[0005] An apparatus, such as circuit, and methods of operation and fabrication are disclosed. A circuit may comprise a triboelectric sensor comprising an output terminal configured to output a voltage pulse based on a contact event. The circuit may comprise a sensing element comprising a first thin film transistor. The first thin film transistor may be configured to receive the voltage pulse and output a signal having a voltage based on the voltage source. The signal may be indicative of a contact force of a contact event. The signal may be indicative of a length of time of the contact event. The signal may comprise a pulse width based on a time length of the contact event. The circuit may comprise a load element electrically coupled to the sensing element and configured to supply the load to the sensing element. The triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

[0006] A circuit may comprise a triboelectric sensor, and a sensing element electrically coupled to the triboelectric sensor and configured to output a signal in response to a change in voltage from the triboelectric sensor. The sensing element may comprise a first thin film transistor electrically coupled to the triboelectric sensor. The circuit may further comprise a load element electrically coupled to the sensing element and configured to supply a load to the sensing element. The triboelectric sensor, the sensing element, and the load element may be disposed on a flexible substrate.

[0007] A circuit may comprise a triboelectric sensor configured to output a change in voltage in response to a contact event, and a readout circuit comprising an array of thin film transistors comprising an amorphous oxide semiconductor, wherein the readout circuit is configured to output a signal indicative of the contact event detected by the triboelectric sensor.

[0008] A method may comprise receiving, by a sensing element from a triboelectric sensor, a voltage signal indicative of a contact event. The sensing element may comprise a thin film transistor. The method may comprise supplying, by a load element electrically coupled to the sensing element, a load to the sensing element. The triboelectric sensor, the sensing element, and the load element may be disposed on a flexible substrate. The method may comprise outputting, by the sensing element, an output signal indicative of the contact event. Brief Description of the Drawings

[0009] The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become apparent and be better understood by reference to the following description of one aspect of the disclosure in conjunction with the

accompanying drawings, wherein:

[0010] FIG. 1 shows an example configuration used as readout circuit of triboelectric sensors.

[0011] FIG. 2A is a diagram illustrating an example readout circuit in accordance with the present disclosure.

[0012] FIG. 2B is a diagram illustrating another example readout circuit.

[0013] FIG. 3 is a diagram illustrating another example circuit.

[0014] FIG. 4 shows an example mask for readout circuit fabrication.

[0015] FIG. 5 is a graph illustrating a transfer curve of thin film transistors with different channel widths.

[0016] FIG. 6 is a graph illustrating the operation of example fabricated transistors.

[0017] FIG. 7 is a graph illustrating output of example fabricated readout circuits for different touch events.

[0018] FIG. 8 is a graph illustrating example output for different touch times.

[0019] FIG. 9 is a graph illustrating readout characteristics for different contact events.

[0020] FIG. 10 is an example method of operating a circuit in accordance with the present disclosure.

Detailed Description

[0021] The present disclosure can be understood more readily by reference to the following detailed description of the disclosure and the Examples included therein. It is also to be understood that the terminology used herein is for describing particular aspects only and is not intended to be limiting.

[0022] Various combinations of elements of this disclosure are encompassed by this disclosure, for example, combinations of elements from dependent claims that depend upon the same independent claim.

[0023] Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification.

[0024] The design and fabrication of a readout circuit for self-powered triboelectric sensors are described herein. The devices comprise thin film transistors that may be based on amorphous oxide semiconductors, such as indium gallium zinc oxide (IGZO) semiconductors as active material. An example structure may be fabricated on flexible substrates (for example, polyimide, a silicon substrate comprising a polyimide thin film layer), which enables the possibility of applications in emerging wearable electronics. Due to the self- powered nature of triboelectric sensors and their operation through charge accumulation on touch events, a variety of readout circuit architectures are disclosed that provide stability and reliability on the read signal of the sensors.

[0025] With the development of Internet of Things (IoT) applications, the need for wireless, sustainable, and independent operation of millions of sensor nodes with different functionalities is becoming increasingly important. Emerging sensor technologies such as triboelectric sensors have raised increased attention from researchers around the world to produce self-powered and reliable sensory platforms. However, due to the extremely low electrical current produced by triboelectric sensors, readout circuits with special capabilities are described herein to translate the sensor’s produced analog signal into a usable digital signal. The use of low-cost thin film technologies to produce flexible readout circuits for triboelectric sensors is described herein.

[0026] The design and fabrication of flexible thin film-based readout circuits that can be used as a signal acquisition interface for triboelectric sensors is disclosed. Due to the nature of thin film deposition and patterning techniques described herein, the circuits described herein may comprise mechanically flexible circuitry seamlessly integrated with flexible triboelectric sensors. The present disclosure may address problems with conventional readout circuits by providing a circuit configuration that is able to detect the triboelectric sensor’s generated voltage pulse and convert it into a voltage signal that can be used in analog to digital converters (ADC).

[0027] FIG. 1 shows a configuration that may be used as readout circuit of triboelectric sensors. Laboratory equipment such as system electrometers, multimeters, oscilloscopes, among other tools are commonly used to produce readings of triboelectric sensors. Laboratory equipment, however, is bulky, not portable, and thus, not suitable for practical applications of triboelectric sensors, such as in wearable devices. The present disclose describes the design and fabrication different standalone architectures for triboelectric sensors readout circuits that address the above problems.

[0028] FIGS. 2A and FIG. 2B shows the schematic integration of the triboelectric sensor with an example of a circuit 200 (for example, a readout circuit). It should be noted that the resistive load used for readout purposes in conventional solutions is eliminated, simplifying the overall system fabrication and improving sensor readout data to allow for press time and press force sensing. As it can be seen from FIG. 2A, the circuit 200 may comprise one or more thin film transistors, such as a first thin film transistor 210, a second thin film transistor 222, and a third thin film transistor 230. However, other configurations may be used. As shown, the first thin film transistor 210 may operate as a sense element and function similar to a regular N-type metal-oxide-semiconductor (NMOS) transistor. The second thin film transistor 222 and/or the third thin film transistor 230 may function as enhancement load transistors. For example, the second thin film transistor 222 and/or the third thin film transistor 230 may function as resistive loads that allow the circuit 200 to produce an output voltage equal to voltage drain VDD (for example, a voltage source 214) and a pulse width equal to the press time of the touch event when a voltage pulse is detected at a gate of the first thin film transistor 210. It is to be noted that similar functionality can be achieved by using both the second thin film transistor 222 and the third thin film transistor 230 or by using a single transistor, however, the use of multiple transistors in this implementation may provide stability and prevent false readings at the output terminal of the readout circuit.

[0029] By way of further explanation, the circuit 200 may comprise a triboelectric sensor 202. The triboelectric sensor 202 may comprise an output terminal 204 configured to output a voltage pulse based on a contact event. The triboelectric sensor 202 may be configured to output a voltage signal (for example, a change in voltage, a voltage pulse) in response to a contact event. The contact event may comprise any contact, such as contact from a user, with the triboelectric sensor 202. For example, the contact event may comprise a touch event, a press event, and/or the like.

[0030] The circuit 200 may comprise a readout circuit 206 (for example, readout stage, readout element). The readout circuit 206 may be configured to output a signal indicative of the contact event detected by the triboelectric sensor 202. The readout circuit 206 may comprise an array of thin film transistors. The array of thin film transistors may have thin film transistors of a variety of types, such as n-type transistors and p-type transistors. Each of the array of thin film transistors may be connected in series (e.g., source connected to drain). A portion of the array of thin film transistors may be configured to sense signals from the triboelectric sensor. Another portion of the array of thin film transistors may be configured as a load.

[0031] The circuit 200 (for example, the readout circuit 206, the array of thin film transistors) may comprise a sensing element 208. The sensing element 208 may be electrically coupled to the triboelectric sensor 202. The sensing element 208 may be configured to output a signal in response to a change in voltage (for example, or a voltage pulse) from the triboelectric sensor 202. The signal may be indicative of the contact event detected by the triboelectric sensor 202.

[0032] The sensing element 208 (for example, the array of thin film transistors) may comprise a first thin film transistor 210. The first thin film transistor 210 may be electrically coupled to the triboelectric sensor 202. The first thin film transistor 210 may be configured to be electrically coupled to a voltage source 214. The first thin film transistor 210 may be configured to receive the voltage pulse (for example, or voltage signal, from the triboelectric sensor 202) and output a signal having a voltage based on a voltage source 214. The voltage of the signal output by the first thin film transistor 210 may have a pulse width based on a time length of the contact event. For example, a longer contact event may cause a wider pulse width. The voltage of the signal output by the first thin film transistor 210 may be based on a force (for example, pressure) of the contact event. For example, a higher force may result in a higher voltage.

[0033] The first thin film transistor 210 may comprise a drain terminal 212. The drain terminal 212 may be configured to be coupled to the voltage source 214. The first thin film transistor 210 may comprise a source terminal 216 electrically coupled to a load (for example, configured to receive a load). The first thin film transistor 210 may comprise a gate terminal 218. The gate terminal 218 of the first thin film transistor 210 may be configured to cause output of a signal (for example, from the readout circuit 206). The signal may comprise a voltage based on the voltage source and a pulse width based on a time length of the contact event. The gate terminal 218 of the first thin film transistor 210 may be configured to cause output of the signal in response to receiving a voltage signal (for example, or change in voltage) from the triboelectric sensor 202. For example, the gate terminal 218 of the first thin film transistor 210 may rely on a field effect to modulate a signal. A voltage signal (for example, voltage pulse) from the triboelectric sensor 202 may be received at the gate terminal 218, causing a fluctuation in the conductivity of a channel of the first thin film transistor 210 between the drain terminal 212 and the source terminal 216. The signal is modulated according to the fluctuation in the conductivity.

[0034] The circuit 200 may comprise a load element 220. The readout circuit 206 may comprise the load element 220. The load element may be electrically coupled to the sensing element 208. The load element 220 may be configured to supply a load to the sensing element 208. For example, the load element 220 may be configured to supply the load to a source terminal 216 of the sensing element (for example, the first thin film transistor 210).

The load element 220 may configure the sensing element 208 to pass current from the voltage source 214 to an output of the sensing element 208. The load element 220 may be configured to prevent the current from the voltage source 214 from passing through the sensing element 208 to a ground 238.

[0035] The load element 220 may comprise one or more thin film transistors electrically coupled to the first thin film transistor 210. The one or more thin film transistors of the load element 220 may comprise a second thin film transistor 222. The second thin film transistor 222 may be electrically coupled to the sensing element 208. The second thin film transistor 222 may be electrically coupled to the first thin film transistor 210. The second thin film transistor 222 may have a drain terminal 224, a gate terminal 226, and a source terminal 228. The drain terminal 224 may be electrically coupled to the source terminal 216 of the first thin film transistor 210.

[0036] The one or more thin film transistors of the load element 220 may comprise a third thin film transistor 230. The third thin film transistor 230 may be electrically coupled to the second thin film transistor 222. The third thin film transistor 230 may comprise a drain terminal 232, a gate terminal 234, and a source terminal 236. The drain terminal 232 of the third thin film transistor 230 may be electrically coupled to the source terminal 228 of the second thin film transistor 222. The gate terminal 234 of the third thin film transistor 230 may be electrically coupled to the source terminal 228 of the second thin film transistor 222. The source terminal 236 may be electrically coupled to a ground 238. The one or more thin film transistors of the load element 220 may function as one or more resistors. For example, each of the one or more transistors of the load element 220 may have a corresponding output resistance (for example, which may be equivalent to resistance). The one or more transistors may function as a series resistance connected to the source terminal 216 of the first thin film transistor 210. For example, coupling the second thin film transistor 222 and the third thin film transistor 230 in the manner shown in FIG. 2A may configure the second thin film transistor 222 and the third thin film transistor 230 to function as resistors in series.

[0037] FIG. 2B shows an example circuit 250 with an alternate load element. The circuit 250 may comprise a load element 252. The load element 252 may comprise a resistor 254. The resistor 254 may comprise a conventional resistor, a thin film resistor, a combination thereof, and/or the like. The resistor 254 may be electrically coupled to the source terminal 216 of the first thin film transistor 210. The resistor 254 may be electrically coupled to the ground 238. The resistor 254 may be used (for example, instead of transistors) in the load element 252 if a simpler fabrication process is preferred. The resistor 254 may be made of an engineered conductor with the appropriate resistivity. The resistor 254 may be used if transistors are not able to reach the desired resistance value.

[0038] FIG. 3 shows another example circuit 300. The circuit 300 may comprise the circuit 200 of FIG. 2A. For example, the circuit 300 may comprise the readout circuit 206 and the triboelectric sensor 202. The readout circuit 206 may be implemented as shown in FIG. 2A or as shown in FIG. 2B. In FIG. 3, the readout circuit 206 is shown as integrated with two additional stages. The readout circuit 206 may have the same functionality as described above but with two more stages added for readout stability. Electric charge accumulation may be produced in the sensing material of the triboelectric sensor causing the readout circuit to occasionally give false outputs until the charges are drained from the triboelectric sensor. For at least this reason or others, an inverter may be used as a buffer stage (for example, buffer element 302) with a non-centered switching threshold. The non- centered switching threshold of the inventor may be controlled (for example, predetermined) based on the geometrical dimensions (for example, channel width and gate length) of the transistors of the inverter. When a voltage pulse is received at the gate terminal 218 of the first thin film transistor 210 an output voltage equal to VDD may be produced at an output terminal of the readout circuit 206 (for example, or the source terminal 216). The buffer stage may receive the readout signal in a gate terminal of a pull down transistor and produce an inverted output at its output terminal. To provide a positive signal when a touch event is detected in the triboelectric sensors, the output of the buffer stage may be inverted. For this reason, an inverting stage (for example, or inverting element 320), which comprises a centered switching threshold inverter, may be connected to the output of the buffer stage as described further below.

[0039] The circuit 300 may comprise a buffer element 302. The buffer element 302 may be configured to filter out charge accumulation from the triboelectric sensor 202 that is not indicative of a contact event. The buffer element 302 may comprise an inverter with a non-centered switching threshold. The buffer element 302 may comprise one or more thin film transistors. The one or more thin film transistors of the buffer element 302 may comprise a bottom thin film transistor 304 electrically coupled to a ground 238. The bottom thin film transistor 304 may comprise a drain terminal 306, a gate terminal 308, and a source terminal 310. The one or more thin film transistors of the buffer element 302 may comprise a top thin film transistor 312. The top thin film transistor 312 may be configured to be electrically coupled to the voltage source 214. The top thin film transistor 312 may comprise a drain terminal 314, a gate terminal 316, and a source terminal 318. As used herein, the terms top and bottom when used to describe a transistor identify the position of the transistor relative to the other circuit elements as shown in a corresponding figure. A top transistor may be the transistor shown closest to the top of the figure. A bottom transistor may be a transistor closer to the bottom of the figure. This usage of top and bottom is for illustration only and the orientation and fabrication of such circuits may not be so limited and may achieve the disclosed functionality.

[0040] The gate terminal 308 of the bottom thin film transistor 304 may be electrically coupled to the source terminal 216 of the first thin film transistor 210. The drain terminal 306 of the bottom thin film transistor 304 may be electrically coupled to the source terminal 318 of the top thin film transistor 312. The source terminal 310 of the bottom thin film transistor 304 may be electrically coupled to the ground 238. The drain terminal 314 of the top thin film transistor 312 may be configured to be electrically coupled to the voltage source 214. The gate terminal 316 of the top thin film transistor 312 may be electrically coupled to the source terminal 318 of the top thin film transistor 312. The transistors of the buffer element 302 may be electrically coupled in the described manner in order to function as an inverter. For example, the transistors of the buffer element 302 may be electrically coupled in the described manner to filter out false signals from the triboelectric sensor.

[0041] The circuit 300 may comprise an inverting element 320. The inverting element 320 may be configured to invert the signal received from the buffer element 302. The inverting element 320 may comprise an inverter with a centered switching threshold. The inverting element 320 may comprise one or more thin film transistors. The one or more thin film transistors of the inverting element 320 may comprise a top thin film transistor 322. The top thin film transistor 322 may comprise a drain terminal 324, a gate terminal 326, and a source terminal 328. The one or more thin film transistors of the inverting element 320 may comprise a bottom thin film transistor 330. The bottom thin film transistor 330 of the inverting element 320 may comprise a drain terminal 332, a gate terminal 334, and a source terminal 336.

[0042] The bottom thin film transistor 330 of the inverting element 320 may be configured to receive the output of the buffer element 302. For example, the bottom thin film transistor 330 may be electrically coupled to one or more of the bottom thin film transistor 304 and the top thin film transistor 312. The gate terminal 334 of the bottom thin film transistor 330 of the inverting element 320 may be electrically coupled to the drain terminal 306 of bottom thin film transistor 304 of the buffer element 302, the gate terminal 316 of the top thin film transistor 312 of the buffer element 302, and/or the source terminal 318 of the top thin film transistor 312 of the buffer element 302. The bottom thin film transistor 330 of the inverting element 320 may be electrically coupled to the ground 238. The source terminal 336 of the bottom thin film transistor 330 of the inverting element 320 may be electrically coupled to the ground 238.

[0043] The bottom thin film transistor 330 of the inverting element 320 may be electrically coupled to the top thin film transistor 322. For example, the drain terminal 332 of the bottom thin film transistor 330 may be electrically coupled to the source terminal 328 and/or the gate terminal 326 of the top thin film transistor 322 of the inverting element 320. The top thin film transistor 322 of the inverting element 320 may be configured to be electrically coupled to the voltage source 214. For example, the drain terminal 324 of the top thin film transistor 322 of the inverting element 320 may be configured to be electrically coupled to the voltage source 214.

[0044] The transistors of the buffer element 302 and/or the inverting element 320 may be coupled in such a manner to prevent false signals from being output by the circuit 300.

Due to the sensitive nature of triboelectric sensors, several false signals can appear due to friction or even charge accumulation in the sensing film. This circuit 300 may comprise a buffer stage that can prevent false signals or charge accumulation signals that can be present in the sensing element 208 from appearing in the output. Here, the buffer stage can be made by two different inverters (for example, the buffer element 302 and the inverting element 320) with different switching thresholds so that the first inverter is only“tumed-on” when an actual touch signal is present.

[0045] The circuit 300 (for example, or the circuit 200) may comprise a processing element configured to determine, based on the signal from the sensing element, one or more of a contact event, a force of the contact event, or a time length of the contact event. For example, various voltage thresholds may be associated with corresponding force levels. The force of a contact event may be determined by matching the voltage with a corresponding force level. The time length may be determined based on a time associated with a beginning of detecting the voltage signal and a time associated with an end of detecting the voltage signal. The processing element may comprise a thin film processor. The processing element may comprise a programmable processor or controller (for example, a microprocessor such as Arduino). A program may be loaded into the processing element (for example, processor/controller). The program may comprise instructions for configuring the processing element to determine, based on a received signal, one or more data values (for example, or metrics), such as the occurrence of a contact event, the force of the contact event, a beginning of a contact event, an end of a contact event, and/or the time length of the contact event. Additionally or alternatively, the processing element may store a history of data values. The processing element may use the history of data values to match the data values to user gestures. If multiple touch events match a pattern, then a command associated with the pattern may be determined. Example commands may comprise menu navigation commands (for example, show display, cycle through different displays or menus, exit menu, select menu), turn on a device, turn off a device, and/or the like.

[0046] The transistors described herein, such as the array of thin film transistors (for example, the first thin film transistor 210, the one or more thin film transistors of the load element 220, the second thin film transistor 222, the third thin film transistor 230), the one or more thin film transistors of the buffer element 302 (for example, the bottom thin film transistor 304, the top thin film transistor 312), the one or more thin film transistors of the inverting element 320 (for example, the top thin film transistor 322, the bottom thin film transistor 330), and/or the like may comprise a semiconductor, such as an oxide

semiconductor or an amorphous oxide semiconductor. The semiconductor (for example, amorphous oxide semiconductor) may comprise amorphous indium gallium zinc oxide, indium zinc oxide, aluminum zinc oxide, gallium zinc oxide, zinc oxide, zinc-tin oxide, a combination thereof, and/or the like. The transistors described herein may comprise any oxide semiconductor comprising zinc, indium, gallium, aluminum, tin, a combination thereof, and/or the like. The transistors described herein may comprise poly crystalline silicon, amorphous silicon, carbon nanotubes, graphene, organic semiconductors, any other thin film material that can act as a semiconductor, and/or a combination thereof.

[0047] The transistors described herein (for example, of the circuit 300, or circuit 200) may be configured as complimentary transistors, such as complimentary oxide semiconductor transistors. The transistors described herein may comprise field effect transistors. For example, the transistors described herein may comprise N-channel transistors and/or P-channel transistors. The first thin film transistor 210 may comprise an N-channel transistor (for example, a metal-oxide-semiconductor field-effect transistor MOSFET). The second thin film transistor 222 may comprise an N-channel transistor. The third thin film transistor 230 may comprise an N-channel transistor. The bottom thin film transistor 304 may comprise an N-channel transistor. The top thin film transistor 312 may comprise a P-channel transistor. The top thin film transistor 322 of the inverting element may comprise a P-channel transistor. The bottom thin film transistor 330 of the inverting element may comprise an N- channel transistor.

[0048] One or more elements of the circuit 300 (for example, or circuit 200) may be disposed on a substrate. The substrate may be a flexible substrate. For example, the substrate may comprise a thin film substrate. The substrate may comprise a suitable polymer, such as polyimide, and silicon comprising a layer of polyimide. The substrate may comprise polyetherimide, polyethylene naphthalate PEN, polyethylene terephthalate PET,

Polycarbonate, one or more thin sheets of metal, and/or a combination thereof. The triboelectric sensor 202, the readout circuit 206, the sensing element 208, the load element 220, the buffer element 302, the inverting element 320, the first thin film transistor 210, the one or more thin film transistors of the load element 220, the second thin film transistor 222, the third thin film transistor 230, the one or more thin film transistors of the buffer element 302 (for example, the bottom thin film transistor 304, the top thin film transistor 312) the one or more thin film transistors of the inverting element 320 (for example, the top thin film transistor 322, the bottom thin film transistor 330), a combination thereof, and/or the like may be disposed on the substrate.

[0049] The disclosure describes a variety of novel features, which may in various aspects include one or more of but are not limited to the following: use of thin film transistors for triboelectric sensors readout circuits, use of oxide semiconductor based thin film transistors for triboelectric touch sensor readout circuits, low temperature process integration, integration of readout circuitry with triboelectric-based touch sensors, elimination of resistors commonly used with triboelectric sensors to produce a read output, custom made triboelectric sensor readout circuit (for example elimination of expensive laboratory equipment), readout circuitry with multiple sensing capabilities (for example, force, touch, press time), mechanically flexible overall system (for example, elimination of conventional CMOS electronics), seamless integration of readout components with flexible triboelectric sensors, use of a buffer layer in the readout circuitry to handle charge accumulation in the triboelectric sensor, all thin film based triboelectric based touch sensor with readout circuitry, and/or the like.

Methods of Making

[0050] In this section, description of the fabrication and characterization of the designed readout circuits for triboelectric sensors is disclosed. Though the following is illustrated using example values, processes, and materials, it is contemplated that other materials, processes, and values may be used according to design specifications.

[0051] Step 1. A substrate (for example, silicon substrate) may be cleaned. The substrate may be cleaned using acetone and isopropanol to eliminate any organic impurities and particles. Then, a polyimide (PI) film (for example, 10 micrometers (microns, pm) thick polyimide film) may be spin coated. For example, the polyimide film may be spin coated at 3000 revolutions per minute (rpm) for 45 seconds. The polyimide film may be thermally cured. The polyimide film may be thermally cured in three different steps: a) 90 seconds at 90 °C; b) ramp from 90 °C to 300 °C with a ramp of 4 °C per minute; and c) 30 minutes at 300 °C and cool down to room temperature.

[0052] Step 2. To prevent the diffusion of oxygen or water molecules from the PI substrate to the devices, aluminum oxide (AI2O3) thin film (for example, about 30 nm) may be deposited on top of the PI film prior to the device fabrication. The AI2O3 film may be deposited using atomic layer deposition (ALD). For example, the AI2O3 may be deposited at 160 °C by atomic layer deposition using a Savannah S200 G2 (Ultratech / Cambridge NanoTech) ALD system. Trimethylaluminum (TMA) from Sigma Aldrich as source of aluminum and deionized water (DIW) as the source of oxygen and N2 (20 standard cubic centimeters per minute, seem) gas may be used as the process gas. 300 cycles (for example, deionized water (DIW) / nitrogen N2-purge/trimethyl amine TMA/ N2-purge) of AI2O3 may be deposited on PI. The pulse time of both TMA and DIW precursor may be fixed as 0.015 seconds and the purge time for N2 may be 5 seconds.

[0053] Step 3. An aluminum doped zinc oxide (AZO) thin film (for example, a thickness of about 170 nanometers, nm) may be used as the gate electrode. The AZO films may be deposited by ALD. For example, the AZO film may be deposited at 160 °C using Diethylzinc (DEZ) and trimethylaluminum (TMA) from Sigma Aldrich as the source of zinc Zn and aluminum A1 and DIW as the source of oxygen. The ratio of DEZ sub-cycle (DIW/N2-purge/DEZ/ N2-purge) to TMA sub-cycle (DIW/ N2-purge /TMA/ N2-purge) may be fixed as 20: 1. The supper cycle [(DIW/N2-purge/DEZ/ N2-purge) + (DIW/ N2-purge /TMA/ N2-purge)] may be repeated 45 times to get AZO films with thickness of about 170 nm. The pulse time for DEZ, TMA and DIW precursor may be fixed as 0.015 seconds and the purge time for N2 may be fixed as 10 seconds.

[0054] Step 4. The gate electrode may be patterned using conventional

photolithography techniques and wet etching. For example, a 4 pm thick ECI 3027 positive photoresist may be coated on top of the substrate at 1750 rpm for 30 seconds and pre-baked at 100 °C for 1 minute. Then, the substrate may be exposed at a constant dose of 200 millijoules per square centimeter (mJ/cm²) using a photolithography mask and developed for 60 seconds in AZ 726 metal-ion free MIF developer. Then the AZO gate electrode may be patterned with diluted hydrochloric acid (for example, 1% in deionized DI water for 35 seconds).

[0055] Step 5. Hafnium oxide (Hf02) (for example, thickness of about 54 nm) may be used as the gate dielectric. The Hf02 gate dielectric layer may be deposited on top of the AZO gate electrodes by ALD technique (for example, using

tetrakis(dimethylamido)hafhium(IV) from Sigma Aldrich as the source of Hf and ozone as the source of oxygen and 90 seem of N2 gas as the process gas). 500 cycles

(tetrakis(dimethylamido)hafhium(IV) / N2-purge /ozone/ N2-purge)] of Hf02 may be deposited on top of the AZO gate electrode. The pulse time of

tetrakis(dimethylamido)hafhium(IV) and ozone may be fixed as 0.2 second and 0.15 second, respectively. The purge time of N2 may be fixed as 10 seconds. The growth temperature for the Hf02 film may be 160 °C. After the Hf02 deposition, the films may post annealed (for example, at 120 °C in air for 2 hours).

[0056] Step 6. An amorphous oxide semiconductor thin film layer may be deposited. For example, Indium gallium zinc oxide (InGaZnO or IGZO) thin film may deposited on top of the HfCh layer. IGZO, or other material, may be deposited by radiofrequency sputtering (for example, Angstrom Engineering) from a 5.08 cm (2 inch, in.) InGaZnO (In:Ga:Zn= 2: 1: 1) target (for example, Super Conductor Materials Inc.) under the deposition conditions as mentioned in Table 1.

Table 1.

Oxygen flow (02)

where *0 p, p total flow (Ar+02)

[0057] Step 7. The semiconductor may be patterned using conventional

photolithography techniques and wet etching. A photoresist may be coated on the substrate and prebaked. For example, 4 pm thick ECI 3027 positive photoresist may be coated on top of the substrate at 1750 rpm for 30 seconds and pre-baked at 100 °C for 1 minute. The substrate may be exposed using a photolithography mask. For example, the substrate may be exposed at a constant dose of 200 mJ/cm² using a photolithography mask and developed for 60 seconds in AZ 726 MIF developer. Then, the IGZO film may be etched using buffered oxide etch (BOE) (for example, for 7 seconds).

[0058] Step 8. A gate dielectric may be patterned using conventional

photolithography techniques and dry etching. A photoresist may be coated on the substrate. The photoresist may be pre-baked. For example, a 4 pm thick ECI 3027 positive photoresist may be coated on top of the substrate at 1750 rpm for 30 seconds and pre-baked at 100 °C for 1 minute. The substrate may be exposed using a photolithography mask. For example, the substrate may be exposed at a constant dose of 200 mJ/cm² using a photolithography mask and developed for 60 seconds in AZ 726 MIF developer. Then, the FlfCh layer may patterned using plasma based reactive ion etching (for example, for 1 minute).

[0059] Step 9. A photoresist may be coated on the substrate and pre-baked. For example, a 4 pm thick ECI 3027 positive photoresist may be coated on top of the substrate at 1750 rpm for 30 seconds and pre-baked at 100 °C for 1 minute. The substrate may be exposed using a photolithography mask. For example, the substrate may be exposed at a constant dose of 200 mJ/cm² using a photolithography mask and developed for 60 seconds in AZ 726 MIF developer. Next, a titanium/gold Ti/Au (10 nm/l50 nm) layer is deposited as source drain electrodes and metal interconnects. Finally, the substrate may be submerged in acetone and sonicated to pattern the electrodes using lift-off technique. [0060] Step 10. The sample may be completed by a post deposition annealing of the stack. The annealing may be performed at 160 °C in air for 2 hours using a conventional tube furnace.

[0061] Step 11. A triboelectric material may be spin-coated, deposited, and/or the like on top of a bottom electrode already patterned in the substrate to complete the stack. For example, a poly[(vinybdenefluoride-co-trifluoroethylene] PVDF-TrFE layer (or any other suitable triboelectric material) may be spin coated (or deposited) on top of the bottom electrode. The P(VDF-TrFE) copolymer (75/25 mol%) may dissolved in dimethyl-formamide (DMF) for 8 hours to have a 20 wt% solution. Then, the solution may be spin coated on the substrate at speed of 1000 rpm, forming a layer of 12.2 pm PVDF-TrFE. After finishing the whole process, the film may be annealed. The film may be annealed in a conventional oven for 4 hours at 135 °C under vacuum.

[0062] Thin film transistors were fabricated using the example parameters above.

FIG. 4 shows the designed mask for readout circuit fabrication. The thin film transistors were characterized to confirm the switching behavior of the thin film transistors. The transistors were characterized using a Keithley semiconductor analyzer and the following terminal parameters:

Gate voltage sweep = -5 to 5 volts (V) in steps of 0.01 V

Drain voltage = 5 V constant

Source voltage = ground GND (0 V)

[0063] FIG. 5 shows the transfer curve of thin film transistors with different channel widths and 10 pm gate length. It can be seen that the transistor provides the expected directly proportional relation between channel width and drain saturation current.

[0064] To confirm the stability of the devices and their potential for AC switching, the thin film transistors were subjected to 5 different sweeps. FIG. 6 confirms the constant operation of the fabricated transistors. It can be seen that there is no significant change in any of the performance parameters of the transistor, as the curves of different sweeps retrace themselves.

[0065] The fabricated readout circuits were characterized using a CASCADE probe station and a Tektronics oscilloscope. First, the readout circuits are placed on the probe station and 10 pm contact tips are landed in the respective contact pads. Then, the external triboelectric sensor is connected to the circuit via Bayonet Neill-Concelman BNC-alligator cables. The oscilloscope is used to measure the voltage change in the output of the fabricated readout circuit. FIG. 7 shows the recorded output of the fabricated readout circuits for different touch events.

[0066] To characterize the compatibility of the readout circuit with applications where press time measurements are important, the readout circuit was characterized for different touch times. FIG. 8 shows the recorded output for different touch times.

[0067] Finally, to characterize the compatibility of the readout circuit with applications where force measurements are important, the readout circuit was characterized for different pressures applied on the triboelectric sensor. FIG. 9 shows the readout characteristics for different applied force/pressure.

[0068] FIG. 10 shows an example method 1000 of operating the circuits described herein. At step 1002, a voltage signal indicative of a contact event may be received. The voltage signal may be received by a sensing element from a triboelectric sensor. The sensing element may comprise a thin fdm transistor. For example, the sensing element may comprise the sensing element 208 of FIG. 2A, FIG. 2B, or FIG. 3. At step 1004, a load may be supplied to the sensing element. The load may be supplied by a load element electrically coupled to the sensing element. The load element may comprise the load element as described further herein. The triboelectric sensor, the sensing element, and the load element may be disposed on a flexible substrate as described further herein. At step 1006, an output signal indicative of the contact event may be output by the sensing element. The output signal may be output to a processor, an integrated circuit, storage, to a buffering element as described further herein.

[0069] The method 1000 may further comprise buffering, by a buffering element, the output signal. Buffering the output signal may comprise inverting the output signal in a first inverting stage. The buffering element may comprise an inverter. For example, the buffering element may comprise the buffer element 302 (for example, or buffering stage) of FIG. 3.

The method 1000 may further comprising inverting a result (for example, or output) of buffering the output signal. The result may be received from an output of the buffering element. The result may be inverted and output to one or more other circuit elements, such as a processor. The processor may determine a signal characteristic, such as contact event, a length of a contact event, and/or a force of a contact event. The signal characteristic may be output via a display (for example, on a wearable device. The signal characteristic may be used to determine an instruction, a metric, and/or the like. The instruction, the metric, and/or the signal characteristic may be stored in storage (for example, of the wearable, or remotely at a server or other user device). Aspects

[0070] The present disclosure relates at least to the following aspects.

[0071] Aspect 1A. A circuit comprising: a triboelectric sensor comprising an output terminal configured to output, based on a contact event, a voltage pulse; a sensing element comprising a first thin film transistor, wherein the first thin film transistor is configured to be electrically coupled to the triboelectric sensor and a voltage source, wherein the first thin film transistor is configured to receive the voltage pulse and output a signal having a voltage based on the voltage source, wherein the signal is indicative of a contact force and a length of time of the contact event; and a load element electrically coupled to the sensing element and configured to supply the load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

[0072] Aspect 1B. A circuit consisting of: a triboelectric sensor comprising an output terminal configured to output, based on a contact event, a voltage pulse; a sensing element comprising a first thin film transistor, wherein the first thin film transistor is configured to be electrically coupled to the triboelectric sensor and a voltage source, wherein the first thin film transistor is configured to receive the voltage pulse and output a signal having a voltage based on the voltage source, wherein the signal is indicative of a contact force and a length of time of the contact event; and a load element electrically coupled to the sensing element and configured to supply the load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

[0073] Aspect 1C. A circuit consisting essentially of: a triboelectric sensor comprising an output terminal configured to output, based on a contact event, a voltage pulse; a sensing element comprising a first thin film transistor, wherein the first thin film transistor is configured to be electrically coupled to the triboelectric sensor and a voltage source, wherein the first thin film transistor is configured to receive the voltage pulse and output a signal having a voltage based on the voltage source, wherein the signal is indicative of a contact force and a length of time of the contact event; and a load element electrically coupled to the sensing element and configured to supply the load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

[0074] Aspect 2. The circuit of any of aspects 1A-1C, wherein the first thin film transistor comprises an amorphous oxide semiconductor. [0075] Aspect 3. The circuit of any of aspects 1A-1C, wherein the load element comprises one or more of a thin film resistor or second thin film transistors electrically coupled to the first thin film transistor.

[0076] Aspect 4. The circuit of any of aspects 1A-1C, further comprising a buffer element comprising one or more third thin film transistors and configured to filter out charge accumulation from the triboelectric sensor that is not indicative of a contact event.

[0077] Aspect 5. The circuit of aspect 4, further comprising an inverting element comprising one or more fourth thin film transistors and configured to invert the signal received from the buffer element.

[0078] Aspect 6. The circuit of aspect 5, wherein the buffer element comprises an inverter with a non-centered switching threshold, and wherein the inverting element comprises an inverter with a centered switching threshold.

[0079] Aspect 7A. A circuit comprising: a triboelectric sensor; a sensing element electrically coupled to the triboelectric sensor and configured to output a signal in response to a change in voltage from the triboelectric sensor, wherein the sensing element comprises a first thin film transistor electrically coupled to the triboelectric sensor; and a load element electrically coupled to the sensing element and configured to supply a load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

[0080] Aspect 7B. A circuit consisting of: a triboelectric sensor; a sensing element electrically coupled to the triboelectric sensor and configured to output a signal in response to a change in voltage from the triboelectric sensor, wherein the sensing element comprises a first thin film transistor electrically coupled to the triboelectric sensor; and a load element electrically coupled to the sensing element and configured to supply a load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

[0081] Aspect 7C. A circuit consisting essentially of: a triboelectric sensor; a sensing element electrically coupled to the triboelectric sensor and configured to output a signal in response to a change in voltage from the triboelectric sensor, wherein the sensing element comprises a first thin film transistor electrically coupled to the triboelectric sensor; and a load element electrically coupled to the sensing element and configured to supply a load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate. [0082] Aspect 8. The circuit of any of aspects 7A-7C, wherein the first thin film transistor comprises one or more of a semiconductor or an amorphous oxide semiconductor.

[0083] Aspect 9. The circuit of aspect 8, wherein the amorphous oxide

semiconductor comprises one or more of zinc, indium, gallium, aluminum, or tin.

[0084] Aspect 10. The circuit of any of aspects 7A-7C, wherein the load element comprises one or more of a thin film resistor or second thin film transistors electrically coupled to the first thin film transistor.

[0085] Aspect 11. The circuit of aspect 10, wherein the one or more second thin film transistors comprise a second thin film transistor having a drain terminal electrically coupled to a source terminal of the first thin film transistor, and wherein the one or more second thin film transistors comprises a third thin film transistor having a drain terminal electrically coupled to the source terminal of the second thin film transistor.

[0086] Aspect 12. The circuit of any of aspects 7A-7C, further comprising a buffer element comprising one or more third thin film transistors and configured to filter out charge accumulation from the triboelectric sensor that is not indicative of a contact event.

[0087] Aspect 13. The circuit of aspect 12, further comprising an inverting element comprising one or more fourth thin film transistors and configured to invert the signal received from the buffer element.

[0088] Aspect 14. The circuit of aspect 13, wherein the buffer element comprises an inverter with a non-centered switching threshold, and wherein the inverting element comprises an inverter with a centered switching threshold.

[0089] Aspect 15 A. A circuit comprising: a triboelectric sensor configured to output a change in voltage in response to a contact event; and a readout circuit comprising an array of thin film transistors comprising an amorphous oxide semiconductor, wherein the readout circuit is configured to output a signal indicative of the contact event detected by the triboelectric sensor.

[0090] Aspect 15B. A circuit consisting of: a triboelectric sensor configured to output a change in voltage in response to a contact event; and a readout circuit comprising an array of thin film transistors comprising an amorphous oxide semiconductor, wherein the readout circuit is configured to output a signal indicative of the contact event detected by the triboelectric sensor.

[0091] Aspect 15C. A circuit consisting essentially of: a triboelectric sensor configured to output a change in voltage in response to a contact event; and a readout circuit comprising an array of thin film transistors comprising an amorphous oxide semiconductor, wherein the readout circuit is configured to output a signal indicative of the contact event detected by the triboelectric sensor.

[0092] Aspect 16. The circuit of any of aspects 15A-15C, wherein the amorphous oxide semiconductor comprises amorphous indium gallium zinc oxide.

[0093] Aspect 17. The circuit of any of aspects 15A-15C, wherein the array of thin film transistors comprises a first thin film transistor configured to sense the change in voltage and output the signal indicative of the contact event, wherein the array of thin film transistors comprises one or more second thin film transistors electrically coupled to a first thin film transistor and configured to supply a load to the first thin film transistor.

[0094] Aspect 18. The circuit of aspect 17, wherein the one or more second thin film transistors comprise a second thin film transistor having a drain terminal electrically coupled to a source terminal of the first thin film transistor, and wherein the one or more second thin film transistors comprises a third thin film transistor having a drain terminal electrically coupled to the source terminal of the second thin film transistor.

[0095] Aspect 19. The circuit of aspect 17, further comprising a buffer element comprising one or more third thin film transistors and configured to filter out charge accumulation from the triboelectric sensor that is not indicative of a contact event.

[0096] Aspect 20. The circuit of aspect 19, further comprising an inverting element comprising one or more fourth thin film transistors and configured to invert a signal received from the buffer element.

Definitions

[0097] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term“comprising” can include the aspects“consisting of’ and“consisting essentially of.” Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.

[0098] As used herein, the term“combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0099] Ranges can be expressed herein as from one value (first value) to another value (second value). When such a range is expressed, the range includes in some aspects one or both of the first value and the second value. Similarly, when values are expressed as approximations, by use of the antecedent‘about,’ it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. For example, if the value“10” is disclosed, then“about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[00100] As used herein, the terms“about” and“at or about” mean that the amount or value in question can be the designated value, approximately the designated value, or about the same as the designated value. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is“about” or“approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[00101] As used herein, the terms“optional” or“optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. For example, the phrase“optional additional additives” means that the additional additives can or cannot be included and that the description includes compositions that both include and do not include additional additives.

[00102] Disclosed are the components to be used to prepare the compositions of the disclosure as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C-E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the disclosure. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific aspect or combination of aspects of the methods of the disclosure.

[00103] References in the specification and concluding claims to parts by weight of a particular element or component in a composition or article, denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.

[00104] A weight percent of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included. As used herein the terms“weight percent,”“wt%,” and“wt. %,” which can be used interchangeably, indicate the percent by weight of a given component based on the total weight of the composition, unless otherwise specified. That is, unless otherwise specified, all wt% values are based on the total weight of the composition. It should be understood that the sum of wt% values for all components in a disclosed composition or formulation are equal to 100.

[00105] Unless otherwise stated to the contrary herein, all test standards are the most recent standard in effect at the time of filing this application. Each of the materials disclosed herein are either commercially available and/or the methods for the production thereof are known to those of skill in the art. It is understood that the compositions disclosed herein have certain functions. Disclosed herein are certain structural requirements for performing the disclosed functions and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.

[00106] Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of“about 0.1% to about 5%” or“about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (for example, 1%, 2%, 3%, and 4%) and the sub-ranges (for example, 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement“about X to Y” has the same meaning as“about X to about Y,” unless indicated otherwise. Likewise, the statement“about X, Y, or about Z” has the same meaning as“about X, about Y, or about Z,” unless indicated otherwise. The term“about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range. The term“substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%,

95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%. While“about” permits some tolerance, a person of ordinary skill in the art would read the specification in light of his knowledge and skill for guidance on the level of that tolerance, and be reasonably apprised to a reasonable degree the metes and bounds of the claims.

[00107] In this document, the terms“a,”“an,” or“the” are used to include one or more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive“or” unless otherwise indicated. The statement“at least one of A and B” has the same meaning as“A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[00108] In the methods described herein, the acts can be carried out in any order without departing from the principles of the disclosure, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[00109] The term“radiation” as used herein refers to energetic particles travelling through a medium or space. Examples of radiation are visible light, infrared light, microwaves, radio waves, very low frequency waves, extremely low frequency waves, thermal radiation (heat), and black-body radiation. The term“UV light” as used herein refers to ultraviolet light, which is electromagnetic radiation with a wavelength of about 10 nanometers (nm) to about 400 nm.

[00110] The term“cure” as used herein refers to exposing to radiation in any form, heating, or allowing to undergo a physical or chemical reaction that results in hardening or an increase in viscosity.

[00111] The term“coating” as used herein refers to a continuous or discontinuous layer of material on the coated surface, wherein the layer of material can penetrate the surface and can fill areas such as pores, wherein the layer of material can have any three-dimensional shape, including a flat or curved plane. In one example, a coating can be applied to one or more surfaces, any of which may be porous or nonporous, by immersion in a bath of coating material.

[00112] The term“surface” as used herein refers to a boundary or side of an object, wherein the boundary or side can have any perimeter shape and can have any three- dimensional shape, including flat, curved, or angular, wherein the boundary or side can be continuous or discontinuous. While the term surface generally refers to the outermost boundary of an object with no implied depth, when the term‘pores’ is used in reference to a surface, it refers to both the surface opening and the depth to which the pores extend beneath the surface into the substrate.

[00113] As used herein, the term“polymer” refers to a molecule having at least one repeating unit and can include copolymers and homopolymers. The polymers described herein can terminate in any suitable way. In some aspects, the polymers can terminate with an end group that is independently chosen from a suitable polymerization initiator, -H, -OH, a substituted or unsubstituted (Ci-C2o)hydrocarbyl (for example, (Ci-Cio)alkyl or (C6-C2o)aryl) interrupted with 0, 1, 2, or 3 groups independently selected from -0-, substituted or unsubstituted -NH-, and -S-, a poly(substituted or unsubstituted (Ci-C2o)hydrocarbyloxy), and a poly(substituted or unsubstituted (Ci-C2o)hydrocarbylamino). [00114] Method examples described herein can be machine or computer- implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code can be tangibly stored on one or more volatile, non- transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (for example, compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[00115] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other aspects can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the

understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may he in less than all features of a particular disclosed aspect. Thus, the following claims are hereby incorporated into the Detailed Description as examples or aspects, with each claim standing on its own as a separate aspect, and it is contemplated that such aspects can be combined with each other in various combinations or permutations. The scope of the disclosure should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

What is Claimed:

1. A circuit comprising :

a triboelectric sensor comprising an output terminal configured to output, based on a contact event, a voltage pulse;

a sensing element comprising a first thin film transistor, wherein the first thin film transistor is configured to be electrically coupled to the triboelectric sensor and a voltage source, wherein the first thin film transistor is configured to receive the voltage pulse and output a signal having a voltage based on the voltage source, wherein the signal is indicative of a contact force and a length of time of the contact event; and

a load element electrically coupled to the sensing element and configured to supply the load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

2. The circuit of claim 1, wherein the first thin film transistor comprises an amorphous oxide semiconductor.

3. The circuit of claim 1, wherein the load element comprises one or more of a thin film resistor or second thin film transistors electrically coupled to the first thin film transistor.

4. The circuit of claim 1, further comprising a buffer element comprising one or more third thin film transistors and configured to filter out charge accumulation from the triboelectric sensor that is not indicative of a contact event.

5. The circuit of claim 4, further comprising an inverting element comprising one or more fourth thin film transistors and configured to invert the signal received from the buffer element.

6. The circuit of claim 5, wherein the buffer element comprises an inverter with a non- centered switching threshold, and wherein the inverting element comprises an inverter with a centered switching threshold.

7. A circuit comprising:

a triboelectric sensor; a sensing element electrically coupled to the triboelectric sensor and configured to output a signal in response to a change in voltage from the triboelectric sensor, wherein the sensing element comprises a first thin film transistor electrically coupled to the triboelectric sensor; and

a load element electrically coupled to the sensing element and configured to supply a load to the sensing element, wherein the triboelectric sensor, the sensing element, and the load element are disposed on a flexible substrate.

8. The circuit of claim 7, wherein the first thin film transistor comprises one or more of a semiconductor or an amorphous oxide semiconductor.

9. The circuit of claim 8, wherein the amorphous oxide semiconductor comprises one or more of zinc, indium, gallium, aluminum, or tin.

10. The circuit of claim 7, wherein the load element comprises one or more of a thin film resistor or second thin film transistors electrically coupled to the first thin film transistor.

11. The circuit of claim 10, wherein the one or more second thin film transistors comprise a second thin film transistor having a drain terminal electrically coupled to a source terminal of the first thin film transistor, and wherein the one or more second thin film transistors comprises a third thin film transistor having a drain terminal electrically coupled to the source terminal of the second thin film transistor.

12. The circuit of claim 7, further comprising a buffer element comprising one or more third thin film transistors and configured to filter out charge accumulation from the triboelectric sensor that is not indicative of a contact event.

13. The circuit of claim 12, further comprising an inverting element comprising one or more fourth thin film transistors and configured to invert the signal received from the buffer element.

14. The circuit of claim 13, wherein the buffer element comprises an inverter with a non- centered switching threshold, and wherein the inverting element comprises an inverter with a centered switching threshold.

15. A circuit comprising :

a triboelectric sensor configured to output a change in voltage in response to a contact event; and

a readout circuit comprising an array of thin film transistors comprising an amorphous oxide semiconductor, wherein the readout circuit is configured to output a signal indicative of the contact event detected by the triboelectric sensor.

16. The circuit of claim 15, wherein the amorphous oxide semiconductor comprises amorphous indium gallium zinc oxide.

17. The circuit of claim 15, wherein the array of thin film transistors comprises a first thin film transistor configured to sense the change in voltage and output the signal indicative of the contact event, wherein the array of thin film transistors comprises one or more second thin film transistors electrically coupled to a first thin film transistor and configured to supply a load to the first thin film transistor.

18. The circuit of claim 17, wherein the one or more second thin film transistors comprise a second thin film transistor having a drain terminal electrically coupled to a source terminal of the first thin film transistor, and wherein the one or more second thin film transistors comprises a third thin film transistor having a drain terminal electrically coupled to the source terminal of the second thin film transistor.

19. The circuit of claim 17, further comprising a buffer element comprising one or more third thin film transistors and configured to filter out charge accumulation from the triboelectric sensor that is not indicative of a contact event.

20. The circuit of claim 19, further comprising an inverting element comprising one or more fourth thin film transistors and configured to invert a signal received from the buffer element.