Fatigue-free bipolar loop treatment to reduce imprint effect in piezoelectric device

In some embodiments, the present disclosure relates to a method for recovering degraded device performance of a piezoelectric device. The method includes operating the piezoelectric device in a performance mode by applying one or more voltage pulses to the piezoelectric device, and determining that a performance parameter of the piezoelectric device has a first value that has deviated from a reference value by more than a predetermined threshold value during a first time period. During a second time period, the method further includes applying a bipolar loop to the piezoelectric device, comprising positive and negative voltage biases. During a third time period, the method further includes operating the piezoelectric device in the performance mode, wherein the performance parameter has a second value. An absolute difference between the second value and the reference value is less than an absolute difference between the first value and the reference value.

BACKGROUND

Piezoelectric devices (e.g., piezoelectric actuators, piezoelectric sensors, etc.) are used in many modern day electronic devices (e.g., automotive sensors/actuators, aerospace sensors/actuators, etc.). One example of a piezoelectric device is a piezoelectric actuator. A piezoelectric actuator can be utilized to create a physical movement that exerts a force on a physical part in a system under the control of an electrical signal. The physical movement generated by the piezoelectric actuator can be utilized to control various kinds of systems (e.g., mechanical systems, optical systems, etc.).

DETAILED DESCRIPTION

A piezoelectric metal-insulator-metal (MIM) device includes a piezoelectric layer arranged between top and bottom electrodes. When a sufficient voltage bias is applied across the top and bottom electrodes, a mechanical strain may be induced in the piezoelectric layer. The mechanical strain may, for example, be used in acoustical, mechanical, and/or optical applications. The change in the structure of the piezoelectric layer may affect other electronic properties in the piezoelectric layer such as permittivity, capacitance, polarization, etc.

Over time, as voltage pulses are applied across the piezoelectric layer during a performance mode of the device, electrical charges may accumulate at an interface between the piezoelectric layer and the top or bottom electrode. The electrical charge accumulation, also known as an imprint effect (e.g., static imprint or dynamic imprint), may degrade device performance of the piezoelectric MIM device. Static imprint may occur after a voltage bias pulse is applied to the piezoelectric MIM device, and then the piezoelectric MIM device is stored for a long period of time. Dynamic imprint may occur after consecutive unipolar bias pulses are applied to the piezoelectric MIM device. For example, if the imprint effect (e.g., static imprint or dynamic imprint) occurs in a piezoelectric MIM device, properties such as the permittivity, capacitance, polarization and/or piezoelectric coefficient, for example, of the piezoelectric layer may significantly change when no voltage bias is applied to the piezoelectric MIM device, thereby degrading the piezoelectric MIM device performance. Thus, degradation of electrical or mechanical properties such as permittivity, capacitance, polarization, piezoelectric coefficient, or the like may be used to quantify a degree of imprint of a piezoelectric MIM device.

Various embodiments of the present disclosure provide a method for recovering or preventing a degraded piezoelectric MIM device. In some embodiments, over a first time period, a piezoelectric device may be operated in a performance mode, which may comprise the application of one or more voltage biases and/storage of the piezoelectric device. A recovery operation comprising a bipolar loop, may be performed after a performance parameter of the piezoelectric device has reached a predetermined threshold value. The predetermined threshold value may indicate that the imprint effect has occurred in the piezoelectric device, or that the imprint effect is about to occur in the piezoelectric device.

Upon detection of the predetermined threshold value, one or more cycles of the bipolar loop may be conducted to recover the degraded piezoelectric device. The bipolar loop may comprise the application of a voltage bias at a first amplitude having a first polarity. The voltage bias is then adjusted to a second amplitude having a second polarity opposite to the first polarity, wherein a magnitude of the first amplitude is equal to a magnitude of the second amplitude. The voltage bias may then be adjusted to a third amplitude equal to zero. The magnitude of the first amplitude, in some embodiments, is less than or equal to an electric coercive field voltage of the piezoelectric device prior to degradation. By applying the bipolar loop to the piezoelectric device, charge accumulation at an interface between the piezoelectric layer and the top or bottom electrode may be reduced, and degraded properties of the piezoelectric device caused by an imprint effect (e.g., static imprint or dynamic imprint) may be recovered. Because the voltage biases of the bipolar loop have amplitudes less than or equal to the electric coercive field voltage of the piezoelectric device, the structure of the piezoelectric device does not experience fatigue. Thus, the bipolar loop may restore or improve reliability of the piezoelectric device performance without degrading the mechanical structure of the piezoelectric device through fatigue.

FIG. 1illustrates a cross-sectional view100of some embodiments of a piezoelectric device coupled to control circuitry.

The piezoelectric device in cross-sectional view100may comprise, in some embodiments, a bottom electrode104over a substrate102. A piezoelectric layer106may be arranged over the bottom electrode104and beneath a top electrode108. In some embodiments, a passivation layer110may be arranged over a top surface of the top electrode108and cover outer sidewalls of the top electrode108, the piezoelectric layer106, and the bottom electrode104. In some embodiments, the bottom electrode104may be wider than the piezoelectric layer106and the top electrode108, and the piezoelectric layer106and the top electrode108may have outermost sidewalls that are substantially aligned with one another. A first metal pad112amay be arranged over the top electrode108and extend through the passivation layer110to directly contact the top electrode108. The first metal pad112ais spaced apart from the piezoelectric layer106and the bottom electrode104by the passivation layer110. In some embodiments, the first metal pad112ais also over the substrate102. A second metal pad112bmay be arranged over the bottom electrode104and extend through the passivation layer110to directly contact the bottom electrode104. In some embodiments, the second metal pad112bis spaced apart from the piezoelectric layer106and/or the top electrode108by the passivation layer110. In some embodiments, the second metal pad112bis also over the substrate102. The second metal pad112bis separated from the first metal pad112a. In some embodiments, electrical contacts114are coupled to each of the first metal pad112aand the second metal pad112b. In some embodiments, the electrical contacts114are solder bumps.

In some embodiments, the first metal pad112aand the second metal pad112beach extend through openings in the passivation layer110. In some embodiments, a width of the openings in the passivation layer110may each be in a range of between about 10 micrometers and about 50 micrometers, about 50 micrometers and about 100 micrometers, about 100 micrometers and about 500 micrometers, about 500 micrometers and about 10 millimeters, and about 10 millimeters and about 100 millimeters. Further, in some embodiments, the passivation layer110, the top electrode108, the piezoelectric layer106, the bottom electrode104, and the first and second metal pads112a,112bmay each have a thickness in a range of between about 10 angstroms and about 100 angstroms, about 100 angstroms and about 100 nanometers, about 100 nanometers and about 1 micrometer, about 1 micrometer and about 100 micrometers, and about 100 micrometers and about 1 millimeter.

Further, in other embodiments of a piezoelectric device, the piezoelectric layer106may be disposed between the top and bottom electrodes108,104. The piezoelectric layer106, the bottom electrode104, and the top electrode108may be surrounded by an inter-layer dielectric layer. Further, in such other embodiments, vias may be coupled to the top and bottom electrodes108,104instead of the first and second metal pads112a,112b.

In some embodiments, control circuitry120may be coupled to the electrical contacts114via wires116. Thus, the control circuitry120may be coupled to the bottom electrode104and the top electrode108. The control circuitry120is configured to apply voltage biases across the piezoelectric layer106via the bottom electrode104and the top electrode108. For example, in some embodiments, the bottom electrode104is grounded, and the control circuitry120is configured to apply voltages to the top electrode108.

In some embodiments, the control circuitry120is configured to operate the piezoelectric device in a performance mode and a recovery mode. The performance mode involves the control circuitry120applying voltage bias pulses across the piezoelectric layer106to induce a mechanical strain in the piezoelectric layer106. During the performance mode, charge carriers may accumulate at a first interface124which is between the piezoelectric layer106and the bottom electrode104, or charge carriers may accumulate at a second interface128which is between the piezoelectric layer106and the top electrode108. For example, in some embodiments, multiple voltage biases having a same polarity may be applied across the piezoelectric layer106by the control circuitry120. Thus, charge carriers may be continuously biased in a certain direction (e.g., from the bottom electrode104to the top electrode108or from the top electrode108to the bottom electrode104) depending on the polarity, and charge carriers may accumulate at the first or second interface124,128, thereby degrading the piezoelectric device performance. In other embodiments, the piezoelectric device may be stored for a long period of time, and charge carriers may accumulate at one of the first or second interfaces124,128, and degrade the piezoelectric device performance.

To improve the piezoelectric device performance, the control circuitry120may be configured to operate in a recovery mode by applying a bipolar loop using bipolar voltage biases that are less than or equal to an electric coercive field voltage of the piezoelectric layer106. In some embodiments, the control circuitry120is configured to apply the bipolar loop multiple times to improve the piezoelectric device performance by decreasing charge carrier accumulation at the first or second interface124,128.

FIG. 2illustrates a cross-sectional view200of some embodiments of a piezoelectric device coupled to measurement circuitry and bias circuitry.

In some embodiments, the control circuitry120ofFIG. 1may comprise bias circuitry210and measurement circuitry220. Thus, in some embodiments, measurement circuitry220and bias circuitry210may be coupled to the top electrode108and the bottom electrode104. Further, in some embodiments, the measurement circuitry220may be coupled to the bias circuitry210. In other embodiments, the measurement circuitry220may be directly coupled to the bias circuitry210, but not directly coupled to the bottom and top electrodes104,108of the piezoelectric device.

In some embodiments, the bias circuitry210may be configured to apply voltage biases of varying magnitudes, polarities, and/or time periods across the piezoelectric layer106to operate in the performance and the recovery modes. The measurement circuitry220may be configured to determine when the bias circuitry210is to operate in the recovery mode. In some embodiments, the measurement circuitry220is configured to detect that a performance parameter of the piezoelectric device has reached or deviated from a predetermined threshold value. For example, in some embodiments, the performance parameter may be an electrical property of the piezoelectric layer106, such as, for example, permittivity, capacitance, polarization, or piezoelectric coefficient. In some embodiments, the predetermined threshold value is before imprint has occurred, whereas in other embodiments, the predetermined threshold value is after imprint has occurred. For example, in some embodiments, the predetermined threshold value may define degradation of capacitance. In such embodiments, the capacitance may be considered degraded when the capacitance of the piezoelectric device has deviated from a reference value by more than the predetermined threshold value, such as, for example, 4 percent. In some embodiments, the reference value may be an initial value of the performance parameter of the piezoelectric device. Nevertheless, once the measurement circuitry220detects degradation, the measurement circuitry220may signal to the bias circuitry210to apply the bipolar loop to recover the piezoelectric device.

In other embodiments, the performance parameter of the piezoelectric device may be a predetermined performance time or a predetermined number of performance pulses. For example, in some embodiments, the measurement circuitry220may count the time that the bias circuitry210has been operating in performance mode. Upon the detection by the measurement circuitry220that the time has reached the predetermined performance time, the measurement circuitry220may signal to the bias circuitry210to apply the bipolar loop to recover the piezoelectric device. For example, in some embodiments, the predetermined performance time may be minutes, hours, days, weeks, etc. Further, in some embodiments, the predetermined number of performance pulses may range from one to thousands of pulses.

In some embodiments, the bias circuitry210is configured to apply the bipolar loop multiple times to increase the recovery of the piezoelectric device. In some embodiments, the number of bipolar loops conducted in a recovery operation by the bias circuitry210is predetermined. In other embodiments, the measurement circuitry220may measure the performance parameter of the piezoelectric device, and detect when the performance parameter has recovered. In some embodiments, recovery of the performance parameter may be based on, for example, a predetermined recovered performance value or a percent improvement between the predetermined threshold value and the performance parameter. In other embodiments, the number of bipolar loops conducted may be based on a predetermined number of loops or a predetermined time period.

FIG. 3illustrates a plot300of some embodiments of a bipolar loop in relation to a hysteresis loop of a piezoelectric device.

Plot300illustrates polarization versus voltage of a piezoelectric device, such as the piezoelectric device illustrated inFIGS. 1 and 2, for example. An electrical coercive field of a piezoelectric material is the maximum electric field that the piezoelectric material can tolerate before becoming depolarized. The plot300inFIG. 3utilizes a thickness of the piezoelectric layer such that the electrical coercive field may be quantified as an electrical coercive field voltage in a hysteresis loop302. The hysteresis loop302represents the change in polarization of a piezoelectric device as the voltage bias applied to the piezoelectric device is increased from zero volts to a first positive voltage316, decreased to a first negative voltage306, and increased back to zero volts, for example. The electrical coercive field voltage of the piezoelectric device is the voltage at which the polarization is equal to zero. In many embodiments, as illustrated inFIG. 3, a piezoelectric device has a positive electric coercive field voltage314and a negative electric coercive field voltage308determined by the hysteresis loop302prior to any imprint effects (e.g., static imprint or dynamic imprint). In some embodiments, the positive electric coercive field voltage314and the negative electric coercive field voltage308are equal in magnitude. For example, in some embodiments, the positive electric coercive field voltage314may be approximately 3 volts, and the negative electric coercive field voltage308may be approximately −3 volts.

In some embodiments, a bipolar loop304is applied to the piezoelectric device in a recovery operation. The maximum voltage bias and minimum voltage bias of the bipolar loop304are determined by the positive electric coercive field voltage314and the negative electric coercive field voltage308, respectively. Thus, in some embodiments, to apply the bipolar loop304to a degraded piezoelectric device, the voltage bias applied to the piezoelectric device by the control circuitry (120ofFIG. 1) may, for example, be increased from a start voltage (e.g., zero volts) to the positive electric coercive field voltage314, decreased to the negative electric coercive field voltage308, and increased to an end voltage (e.g., zero volts) equal to the start voltage. In other embodiments, the bipolar loop304has a maximum voltage that is less than the positive electric coercive field voltage314and a minimum voltage that is greater than the negative electric coercive field voltage308. Thus, the maximum and minimum voltages of the bipolar loop304equal to or between the positive electric coercive field voltage314and the negative electric coercive field voltage308to recover the degraded piezoelectric device while preventing fatigue in the piezoelectric layer106.

FIG. 4illustrates a timing diagram400of some embodiments where a bipolar loop is applied after consecutive unipolar pulses applied to a piezoelectric device.

In some embodiments, during a performance mode, control circuitry (120ofFIG. 1) may apply multiple unipolar pulses402. Each pulse404of the multiple unipolar pulses402may have a first amplitude that is sustained over a first time period t1. In some embodiments, as illustrated inFIG. 4, the first amplitude may be equal to the first positive voltage316, for example, or in some embodiments, equal to the first negative voltage306. In other embodiments, the first amplitude may be greater than or less than the first positive voltage316. In some embodiments, the first positive voltage316may be greater than the positive electric coercive field voltage314, and the first negative field voltage306may be less than the negative electric coercive field voltage308. However, increasing the first amplitude may increase the rate of degradation of performance parameters of the piezoelectric device. Further in some embodiments, each pulse404may have the same first amplitudes and/or first time periods t1, whereas in other embodiments, the first amplitude and/or the first time period t1of each pulse404may be different. However, each pulse404has a same polarity, which may cause dynamic imprint in a piezoelectric device.

Thus, in some embodiments, after multiple unipolar pulses402have been applied to a piezoelectric device over a second time period t2, a recovery operation comprising the bipolar loop304may be applied to the piezoelectric device such to recover or prevent the piezoelectric device from the dynamic imprint effect. To conduct the bipolar loop304, control circuitry (120ofFIG. 1) may increase a voltage bias applied to the piezoelectric device to a second amplitude having a first polarity that is sustained for a fourth time period t4, decrease the voltage bias to a third amplitude having a second polarity that is sustained for the fourth time period t4, and increase the voltage bias from the third amplitude to zero. In some embodiments, the second amplitude equals the third amplitude, and the first polarity is opposite to the second polarity. The first and second amplitudes have magnitudes that are less than or equal to magnitudes of the positive and negative electric coercive field voltages308,314of the piezoelectric device. InFIG. 4, the positive electric coercive field voltage314is applied first, and then the negative electric coercive field voltage308may be applied. In other embodiments, the negative electric coercive field voltage308may be applied first, and then the positive electric coercive field voltage314may be applied. Nevertheless, the bipolar loop304over a third time period t3may be applied after multiple unipolar pulses402have been applied to a piezoelectric device to recover a piezoelectric device from dynamic imprint effects.

FIG. 5illustrates a timing diagram500of some embodiments where a bipolar loop is applied after a piezoelectric device undergoes a long storage time to recover the piezoelectric device.

In some embodiments, during a performance mode, control circuitry (120ofFIG. 1) may apply a static sequence502comprising a pulse504followed by a long storage time step506to a piezoelectric device. Like each pulse404inFIG. 4, in some embodiments, the pulse504inFIG. 5may have a first amplitude that is sustained over the first time period t1. In some embodiments, the first amplitude is equal to the first positive voltage316, for example, or the first negative voltage306. In other embodiments, the first amplitude may be greater than or less than the first positive voltage316, or greater than or less than the first negative voltage306. After the first time period t1, the control circuitry (120ofFIG. 1) may not apply a voltage bias to the piezoelectric device for a fifth time period t5during a long storage time step506. In some embodiments, the fifth time period t5may be greater than the first time period t1. Nevertheless, in some embodiments the long storage time step506(e.g., Q-time) may cause static imprint in a piezoelectric device, thereby degrading properties of the piezoelectric device. In some embodiments, to restore the degraded properties of the piezoelectric device from the static imprint effect, the bipolar loop may be performed over the third time period t3after the long storage time step506.

FIG. 6illustrates a timing diagram600of some embodiments where a bipolar loop is applied before a piezoelectric device undergoes a long storage time to prevent degradation in a piezoelectric device.

The timing diagram600ofFIG. 6comprises the same pulse504, bipolar loop304, and long storage time step506as in the timing diagram500ofFIG. 5, except that inFIG. 6, the bipolar loop304is conducted before the long storage time step506. In some embodiments, the bipolar loop304is conducted before the long storage time step506to prevent the static imprint effect from occurring in a piezoelectric device by reducing the polarization and therefore charge accumulation at a first or second interface (e.g.,124,128) of the piezoelectric device during the long storage time step506.

FIG. 7Aillustrates a plot700A of some embodiments of degradation, imprint, and recovery of permittivity of a piezoelectric device.

The plot700A inFIG. 7Acomprises multiple permittivity data points606for each “test number.” In some embodiments, a test may comprise multiple unipolar pulses (402ofFIG. 4), a static sequence (502ofFIG. 5), or a combination thereof. For example, in some embodiments, a test may comprise multiple unipolar pulses (402ofFIG. 4) followed by a long storage time step506. After each test, the permittivity or some other performance parameter of a piezoelectric device may be measured at zero volts and recorded on the plot700A as a permittivity data point606. A first group702of the permittivity data points606illustrates how over time, the permittivity of a piezoelectric device decreases. However, between the first group702and a second group602, the permittivity of a piezoelectric device significantly decreases to an imprinted permittivity706, and remains constant throughout the permittivity data points606of the second group602. Thus, an imprint effect (e.g., static imprint or dynamic imprint) may have occurred between the last test of the first group702and a first test of the second group602.

In some embodiments, at the end of the second group602, a recovery operation604comprising bipolar loops (e.g.,304ofFIG. 4) may increase the permittivity of the piezoelectric device. Although the recovery operation604may not fully recover the permittivity of the piezoelectric device to an initial permittivity708, the recovery operation604may increase the permittivity of the piezoelectric device from the imprinted permittivity706to a recovered permittivity707. In some embodiments, the imprinted permittivity706is ten percent lower than the initial permittivity708. Thus, although the permittivity data points606may not be as high in a third group after the recovery operation604than the permittivity data points606in the first group702, the recovery operation604still improves performance parameters of the piezoelectric device after imprint effects.

FIG. 7Billustrates a timing diagram700B of some embodiments of performing a bipolar loop to recover a piezoelectric device after static imprint.

The timing diagram700B ofFIG. 7Bmay correspond to the plot700A ofFIG. 7A. For example, in some embodiments, each permittivity data point606ofFIG. 7Amay represent the measured permittivity of a piezoelectric device after each static sequence502. Thus, in the first group702ofFIG. 7A, there are nine permittivity data points606, and in the first group702ofFIG. 7B, there are nine static sequences502. In some embodiments, the first group702of static sequences502may occur over a sixth time period t6, and the second group602of static sequences502may occur over a seventh time period t7. Between the first and second groups702,602, a static imprint effect may occur. To recover the piezoelectric device from the static imprint effect, the recovery operation604may comprise more than one bipolar loop304. For example, as illustrated inFIG. 7B, ten bipolar loops304are conducted over an eighth time period t8in the recovery operation604. In other embodiments, a total number of bipolar loops304in a recovery operation604may be in a range of between approximately one bipolar loop304and approximately 100 bipolar loops304.

In some embodiments, a total number of bipolar loops304conducted in a recovery operation604is dependent how much time can be spared, how much recovery is desired, and/or the amount of power available, for example. In some embodiments, each bipolar loop304occurs over the third time period t3that is equal to approximately 40 milliseconds, for example. In some embodiments, the bipolar loops304continue until measurement circuitry (220ofFIG. 2) determines that a predetermined recovered performance value has been reached, or a percent improvement between the predetermined threshold value and the performance parameter has been reached. The predetermined recovered performance value may be based on a measurement of a performance parameter of the piezoelectric device, the eighth time period t8, or a number of bipolar loops, for example. Thus, by using one or more bipolar loops304in a recovery operation604, properties of a degraded piezoelectric device due to an imprint effect may be improved.

FIG. 7Cillustrates a timing diagram700C of some embodiments of performing a bipolar loop to recover a piezoelectric device after dynamic imprint.

The timing diagram700C ofFIG. 7Cmay correspond to the plot700A ofFIG. 7A. For example, in some embodiments, each permittivity data point606ofFIG. 7Amay represent the measured permittivity of a piezoelectric device after each set of multiple unipolar pulses402. In some embodiments, each set of multiple unipolar pulses402may comprise three pulses (404ofFIG. 4), whereas in other embodiments, each set of multiple unipolar pulses402may comprise more than or less than three pulses (404ofFIG. 4). In the first group702ofFIG. 7A, there are nine permittivity data points606, and in the first group702ofFIG. 7C, there are nine sets of multiple unipolar pulses402. Between the first and second groups702,602, a dynamic imprint effect may occur. To recover the piezoelectric device from the dynamic imprint effect, the recovery operation604may comprise more than one bipolar loop304.

FIG. 8Aillustrates a plot800A of some embodiments of recovery of permittivity of a piezoelectric device prior to imprint effects.

The plot800A ofFIG. 8Aillustrates how the recovery operation604may be applied after the first group702but before the second group (602ofFIG. 7A) such that the piezoelectric device may recover before an imprint effect (e.g., static imprint or dynamic imprint) occurs. Although the imprint effect has not fully occurred, as shown in the second group (602ofFIG. 7A), the permittivity of the piezoelectric device may still degrade. In some embodiments, by preventing the imprint effect, the recovery operation604may be more effective in improving degraded device performance of a piezoelectric device.

In some embodiments, the recovery operation604may be applied to a piezoelectric device because the intermediate permittivity710or some other performance parameter of the piezoelectric device has reached a performance parameter predetermined threshold value. In other embodiments, the recovery operation604may be applied to the piezoelectric device because the intermediate permittivity710of the piezoelectric device has deviated from the initial permittivity708(e.g., reference value) by more than a performance parameter predetermined threshold value. In some embodiments, the measurement and determination of device degradation may be performed by measurement circuitry (220ofFIG. 2). In yet other embodiments, when a total number of pulses or a time period has reached a predetermined threshold value while the piezoelectric device is in performance mode during the first group702, the recovery operation604may be conducted to prevent the imprint effect (e.g., static imprint or dynamic imprint).

FIG. 8Billustrates a timing diagram800B of some embodiments of performing a bipolar loop prior to degradation of a piezoelectric device via static imprint.

The timing diagram800B ofFIG. 8Bmay correspond to the plot800A ofFIG. 8A. For example, in some embodiments, each permittivity data point606ofFIG. 8Amay represent the measured permittivity of a piezoelectric device after each static sequence502. Thus, in the first group702ofFIG. 8A, there are nine permittivity data points606, and in the first group702ofFIG. 8B, there are nine static sequences502. However, a last one802of the static sequences502may not comprise the long storage time step506.

In some embodiments, because the recovery operation604is conducted before the static imprint effect, less bipolar loops304may be used in the recovery operation604than if the recovery operation604was performed after the static imprint effect (e.g.,FIG. 7B). In embodiments, to better improve the piezoelectric device, a same or a higher number of bipolar loops304may be used in the recovery operation604when conducted before the static imprint effect than the number of bipolar loops304conducted after a static imprint effect.

FIG. 8Cillustrates a timing diagram700B of some embodiments of performing a bipolar loop prior to degradation of a piezoelectric device via dynamic imprint.

The timing diagram800C ofFIG. 8Cmay correspond to the plot800A ofFIG. 8A. For example, in some embodiments, each permittivity data point606ofFIG. 8Amay represent the measured permittivity of a piezoelectric device after each set of multiple unipolar pulses402. Thus, in the first group702ofFIG. 8A, there are nine permittivity data points606, and in the first group702ofFIG. 8B, there are nine sets of multiple unipolar pulses402. In some embodiments, to prevent dynamic imprint from occurring and to improve any performance parameters of the degraded piezoelectric device, the recovery operation604may be conducted after the first group702.

FIG. 9illustrates a flow diagram of some embodiments of a method900of performing a bipolar loop to a piezoelectric device upon detection of a performance parameter reaching a predetermined threshold value.

At act902, a piezoelectric device is operated in performance mode by applying one or more voltage pulses at a first amplitude to the piezoelectric device.FIG. 4illustrates a timing diagram400of some embodiments corresponding to act902.

At act904, a determination that a performance parameter of the piezoelectric device has reached a predetermined threshold value is performed.

At act906, a bipolar loop is applied to the piezoelectric device by performing acts906a,906b, and906c.

At act906a, a first voltage bias is applied to the piezoelectric device, wherein the first voltage bias has a first polarity and a second amplitude.

At act906b, the first voltage bias is adjusted to a second voltage bias, wherein the second voltage bias has the second amplitude and a second polarity opposite to the first polarity.

At act906c, the second voltage bias is adjusted to a third voltage bias equal to zero.FIGS. 8A, 8B, and 8Cillustrate a plot800A, a timing diagram800B, and a timing diagram800C, respectively, of some embodiments corresponding to acts904,906,906a,906b, and906c.

Therefore, the present disclosure relates to a method of performing a bipolar loop to a piezoelectric device to prevent an imprint effect or recover after an imprint effect to reduce degradation and increase reliability of a piezoelectric device.

Accordingly, in some embodiments, the present disclosure relates to a method for recovering degraded device performance of a piezoelectric device, the method comprising: operating the piezoelectric device in a performance mode over a first time period by applying one or more voltage pulses greater than or equal to a first amplitude to the piezoelectric device; determining during the first time period that a performance parameter of the piezoelectric device has a first value that has deviated from a reference value by more than a predetermined threshold value; applying a bipolar loop to the piezoelectric device over a second time period comprising positive and negative voltage biases, the second time period being after the first time period; and operating the piezoelectric device in the performance mode over a third time period after the second time period, wherein the performance parameter of the piezoelectric device has a second value during the third time period, and wherein an absolute difference between the second value and the reference value is less than an absolute difference between the first value and the reference value.

In other embodiments, the present disclosure relates to a method for preventing degraded device performance of a piezoelectric device, the method comprising: operating the piezoelectric device in a performance mode over a first time period by applying one or more voltage pulses greater than or equal to a first amplitude to the piezoelectric device, wherein the first amplitude is greater than an electric coercive field voltage of the piezoelectric device; determining that a predetermined threshold value of the performance mode has been reached; and performing a bipolar loop to the piezoelectric device over a second time period by: applying a voltage bias signal across the piezoelectric device at a second amplitude at a first polarity; adjusting the voltage bias signal across the piezoelectric device from the second amplitude to a third amplitude at a second polarity opposite to the first polarity, wherein the second amplitude is equal to the third amplitude, and wherein the second amplitude is less than or equal to the electric coercive field voltage of the piezoelectric device; and adjusting the voltage bias signal across the piezoelectric device from the third amplitude to a fourth amplitude that is between the second amplitude and the third amplitude.

In yet other embodiments, the present disclosure relates to a system, the system comprising: a piezoelectric device disposed on a semiconductor substrate, the piezoelectric device comprising a piezoelectric structure disposed between a first electrode and a second electrode; bias circuitry electrically coupled to the first electrode and the second electrode, wherein the bias circuitry configured to operate in a performance mode by applying a voltage bias across the piezoelectric structure; measurement circuitry electrically coupled to the bias circuitry, wherein the measurement circuitry is configured to detect that a predetermined threshold value has been reached during the performance mode; and wherein the bias circuitry is configured to perform a recovery operation upon detection of the predetermined threshold value by: increasing the voltage bias from a start value to a first magnitude at a first polarity, decreasing the voltage bias from the first magnitude at the first polarity to the first magnitude at a second polarity opposite to the first polarity, and increasing the voltage bias from the first magnitude at the second polarity to an end value equal to the start value.