EP3733311A1 - Betätigung eines piezoelektrischen strukturen mit ferroelektrischer dünnschichten mit mehreren elementen - Google Patents

Betätigung eines piezoelektrischen strukturen mit ferroelektrischer dünnschichten mit mehreren elementen Download PDF

Info

Publication number
EP3733311A1
EP3733311A1 EP19172189.3A EP19172189A EP3733311A1 EP 3733311 A1 EP3733311 A1 EP 3733311A1 EP 19172189 A EP19172189 A EP 19172189A EP 3733311 A1 EP3733311 A1 EP 3733311A1
Authority
EP
European Patent Office
Prior art keywords
type
piezoelectric
electrode
signal
elements
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19172189.3A
Other languages
English (en)
French (fr)
Inventor
Paul Muralt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ecole Polytechnique Federale de Lausanne EPFL
Original Assignee
Ecole Polytechnique Federale de Lausanne EPFL
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ecole Polytechnique Federale de Lausanne EPFL filed Critical Ecole Polytechnique Federale de Lausanne EPFL
Priority to EP19172189.3A priority Critical patent/EP3733311A1/de
Priority to PCT/IB2020/054206 priority patent/WO2020222212A1/en
Publication of EP3733311A1 publication Critical patent/EP3733311A1/de
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0688—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF
    • B06B1/0692—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction with foil-type piezoelectric elements, e.g. PVDF with a continuous electrode on one side and a plurality of electrodes on the other side

Definitions

  • the present invention relates to piezoelectric micro-machined ultrasonic transducers (pMUT), particularly for the case of using ferroelectric thin films as piezoelectric elements.
  • FIG. 1 shows a generic type in the form of a cantilever (cross section) containing a piezoelectric thin film 103 sandwiched between a top electrode 101 and a bottom electrode 104, thus forming a parallel plate capacitor.
  • This functional unit is attached to an elastic layer 106, frequently and optionally through a buffer or adhesion layer 105, the elastic layer 106 being attached to a micromachined substrate 107.
  • the elastic layer 106 is bent when an electric field is applied across the piezoelectric thin film 103.
  • the elastic layer 106 is normally at least as thick as the piezoelectric thin film 103 in order to place the neutral plane of the bent structure outside the piezoelectric layer, i.e. inside the elastic layer 106.
  • the working principle is based on the in-plane mechanical stress ( T 1 , T 2 ) generated by the piezoelectric effect upon application of an electric field.
  • this electric field E is perpendicular to the plane (indicated by arrows between the top and bottom electrodes 101 and 104 in figure 1 ), thus having only component 3, i.e., in direction 3 of the coordinate axes drawn in figure 1 and represented as E 3 in figure 2 .
  • the in-plane stress is governed by an effective piezoelectric coefficient e 31 , f , whose derivation 3,4 , and measurement 5,6 are found in the literature.
  • the plate When dealing with excursions of plates and bridges, it is easily seen that the plate must have regions with positive curvature, and regions with negative curvature. For instance, a circular plate deflecting upwards in the center has there a negative curvature, and consequently a positive curvature at the border where it is clamped (i.e., the first derivative of the deflection function is zero at the border). Theoretically, one could soften this border by etching trenches or by partial liberation, but in practice, one has to avoid building too fragile structures, and often an air-tight membrane is required.
  • the changes of curvature may be preselected by the electric field, which can be chosen parallel and antiparallel to the internal polarization of the material, leading to regions with positive and negative stress, and positive and negative curvatures.
  • An example configuration of a piezoelectric laminated plate is sketched as a cross section of a round clamped plate in figure 3 .
  • the schematic illustration of the cross section shows that this has two types of top electrodes mounted on a piezoelectric thin film 303, i.e., a first type of top electrode 301 and a second type of top electrode 302, and a bottom electrode 304 of floating or grounded type.
  • the second type of top electrode 302 being for example a central electrode and the first type of electrode 301 being for example an external, ring-shaped electrode, and the bottom electrode 304 being for example a common bottom electrode that is floating, or at ground.
  • Giving a negative voltage to the central electrode and a positive voltage to the outer electrode leads to compressive stress below the former, and to tensile stress below the latter if the polarization is fixed as indicated by an arrow 303a.
  • Condition is that the internal polarization is stable and does not change with the electric field. This is the case in polar materials that are not ferroelectric.
  • FIG. 3 further shows at least a buffer layer 305, an elastic layer 306 and a micromachined substrate 307.
  • the present invention relates to devices with ferroelectric thin films.
  • Ferroelectric films of PZT Pb(Ti,Zr)O 3
  • PZT Pb(Ti,Zr)O 3
  • the disadvantage of ferroelectric thin films is the ferroelectric switching occurring at a so-called coercive field E c .
  • Figure 4 shows the generated in-plane stress as a function of the electric field.
  • FIG. 4 shows a comparison of piezoelectric performance of ferroelectric thin film 401 and 402, with non-ferroelectric, polar piezoelectric thin films 403, 404, 405, and 406. The latter show a linear behavior across the complete range from strongly negative to strongly positive electric field.
  • the ferroelectric thin films switch as soon as the electric field is larger than about 20 to 50 kV/cm.
  • the polarization is always parallel to the applied electric field, and thus the in-plane stress becomes positive (branches 401, 402) for both signs of the electric field.
  • PZT is not the only possible ferroelectric thin film material.
  • Suitable ferroelectric materials are oxides of the general formula ABO 3 , with the three categories of di-valent Atom A (Pb 2+ , Ba 2+ ) combined with a 4-valent cation B (Ti 4+ , Zr 4+ ), tri-valent Atom A (Bi 3+ ) combined with a tri-valent cation B (Fe 3+ ) (BiFeO 3 ), and mono-valent A (Li + , K +1 , Na +1 ), combined with a 5-valent B (Nb +5 , Ta +5 , W +5 ), as in LiNbO 3 or KNbO 3 . Many of these compounds form solid solutions among each other and are optimized for highest properties often along so-called morphotropic phase boundaries.
  • the buffer or adhesion layers play a role (105, 305, 1505). They may play additional roles as chemical barriers, for texturing the electrode material, and for promoting the growth of the ferroelectric thin film outside the electrode area.
  • Suitable buffer layers can be TiO 2 , ZrO 2 , Ta 2 O 5 , ZnO, Al 2 O 3 , and MgO.
  • Suitable electrodes deposited before the ferroelectric thin film are Pt with (111)-texture, LaNiO 3 and SrRuO 3 with (100) texture, or other, similar conducting perovskite oxide thin films.
  • the top electrodes are from the same materials, or additionally made of aluminum, or gold. In the latter case, chromium or TiW adhesion layers might be applied.
  • the piezoelectric element may be driven by a unipolar voltage (see figure 5 , representing a unipolar operation of ferroelectric thin film of PZT, in which the ferroelectric material is never depolarized by a field in opposite direction of the internal polarization of the ferroelectric material).
  • the advantage of such operation is a better stability of the internal polarization and thus of the piezoelectric coefficients.
  • the stability can even be improved by a so-called poling step including the application of a high field at higher temperature (e.g. 150 °C) (see, e.g. ref. 15 ).
  • This mode is a good solution for linear actuators.
  • MUT Micro-machined Ultrasonics Transducers
  • the MUTs find their justification in large arrays. Indeed, micro fabrication is more suited for miniaturization and for the fabrication of probe arrays with many elements.
  • the only known MUT principles able to reach such high values are those based on electrostatic attraction in the capacitance formed by a membrane and a counter electrode separated by a vacuum cavity of about 10 nanometers. This MUT is called c-MUT. 17
  • the MUT principle employing a piezoelectric thin film - a so called pMUT - was also investigated for a while by the interested community, but was unable to reach high enough coupling factors.
  • FIG. 7 shows one of the best results ever achieved to the date of the present invention (from the research group of the inventor).
  • the coupling coefficient increased up to 11 % because in this case a dc bias was superimposed to the ac signal, in order to avoid polarization switching (unpublished result).
  • the element had only one top electrode covering the central part up to 0.7 times the radius.
  • Part (a) on the left side contains a measured susceptance curve (lm(Y)), wherein the large negative value is to be noted.
  • Part (b) on the right side shows a schematic cross section through the device.
  • the diameter of the diaphragm is 200 ⁇ m
  • the device layer of the SOI silicon on insulator
  • the PZT film is 4 ⁇ m thick. This curve is published for the first time in the present patent application, but the device is from the same batch as those published in refs 15 16 .
  • the electrode version was of type CE. Echo experiments with pMUT's based on PZT thin films were made earlier by the research group of the present inventor, and showed the feasibility of such devices. 9 Figure 8 shows an experiment carried out in air.
  • the acoustic wave was generated with one transducer (called emitter in figure 8 ) and received with a second one (called receiver in figure 8 ). It can be seen that the received signal starts to rise about 100 ⁇ s after the emitted signal started to be generated. This is the signal of the wave that travelled the distance once (indeed, the sound velocity in air corresponds to about 3 cm per 100 ⁇ s).
  • the weaker signals received afterwards repeat themselves with a period of about 180 ⁇ s, corresponding to travel times of about 6 cm, i.e., twice the distance between the devices.
  • One can conclude that the sound wave is reflected at the receiving pMUT, again reflected at the passive emitter pMUT surface, and detected again by the receiver.
  • Figure 8 shows 3 echos, corresponding to a total path of 21 cm. It is therefore quite plausible that the wave can be detected at distances of over 30 cm, as claimed in the article.
  • figure 8 shows an echo experiment with 2 pMUTs.
  • FIG 8(a) the schematic of the experimental set-up is shown; and figure 8(b) is a screen shot of signals.
  • a first pMUT is emitting a short pressure wave burst (5 cycles in this case).
  • the upper curve in figure 8a shows the drive signal given to the emitter (actuator).
  • the lower curve shows the signal captured by the receiver (sensor) after amplification by a charge amplifier.
  • Both pMUTs were fabricated in the same batch and work at identical frequency of 98 kHz.
  • the received signal shows some ringing, i.e., it is longer than the original signal supplied to the emitter. It is also seen that several echoes are received. The wave goes back and forth between emitter and receiver.
  • the aim of this invention is to enhance the performance of pMUT structures with ferroelectric thin films, to create operation conditions at which ferroelectric films may be used at their superior value as material for high piezoelectric stress development, and overall to boost pMUT properties.
  • the invention provides a method for driving piezoelectric elements of a micro-system, the piezoelectric elements comprising a ferroelectric thin film, the piezoelectric elements being configured to be part of any one or a combination of items of a list comprising: a cantilever, a bridge, a diaphragm, a manifold of complex patterns of plates that may include trenches, slits, and include plate elements having different thickness; and the piezoelectric elements being further configured to comprise at least 2 types of parallel plate electrode capacitors, the first type of capacitor having on a first side of the ferroelectric thin film a first type of electrode and the second type of capacitor having a second type of electrode electrically disjoined from the first type of electrode, forming a patterned surface of electrodes of the first side, and the first and second type of capacitors having a common electrode on a second side of the ferroelectric thin film opposite to the first side, and configured to face both the first type of electrode and the second type of electrode.
  • the ferroelectric thin film is fixed on an elastic layer, forming together an elastic structure.
  • the method comprises exciting in at least an exciting burst of an alternating electrical driving signal distributed to a first and a second signal, each active in different halves of the vibration period, and of one polarity only, thus substantially zero, in the other half period when it is not active, whereby the first and the second signal may have either one of the same polarity in their active half period, or opposite polarity, the first signal driving the first type of capacitor during a first half of a vibration period, and the second signal driving the second type of capacitor during a second half of the vibration period, thereby enabling an excitation of a flexural elastic structure, therewith enabling a deformation of the elastic structure, whereby further the vibration period is configured to correspond to a basic resonance of the elastic structure, the exciting burst comprising a determined number of resonance cycles.
  • the step of exciting comprises excitations' duration shorter than a half period, the duration being defined as period/n, where n is an integer.
  • the alternating electrical driving signal is derived from an AC or RF source through a simple device containing diodes for splitting the signal into a branch with negative voltages, and a branch with positive voltages.
  • a thickness of the piezoelectric thin film ranges from 10 nm to 10 ⁇ m.
  • the elastic layer of the flexural structure is a thin film single or multilayer comprising Si 3 N 4 /SiO 2 , SiC, or machined from a silicon substrate using silicon micromachining in techniques with dry etchers and silicon on insulator (SOI) substrates.
  • the invention provides an acoustic device, comprising an elastic layer supporting at least 2 types of parallel plate electrode capacitors formed with a piezoelectric thin film on one side of the elastic layer, the elastic layer being anchored with anchors in a frame structure consisting mainly of a thicker substrate material, the piezoelectric thin film comprising ferroelectric materials; wherein the first type of parallel plate electrode capacitor has on a first side a first type of electrode and the second type of parallel plate electrode capacitor has a second type of electrode electrically disjoined from the first type of electrode, and the first and second type of parallel plate electrode capacitors have a common electrode on a second side opposite to the first side, and configured to face both the first type of electrode and the second type of electrode; wherein the common electrode carries the piezoelectric film, which comprises on its surface opposite to the common electrode the first type and the second type of electrodes that are separated on the surface, and wherein a shape of each of the first and the second of the electrodes follows a required distribution of signs of cur
  • the anchors are a determined number of narrow bridges.
  • each of the anchors comprises a complete clamping around a border of the elastic layer.
  • the piezoelectric film is either one of polar or ferroelectric nature.
  • a thickness of the piezoelectric thin film ranges from 10 nm to 10 ⁇ m.
  • the elastic layer of the flexural structure is a thin film, a single or multilayer comprising Si 3 N 4 /SiO 2 , SiC, or machined from a silicon substrate using silicon micromachining in techniques with dry etchers and silicon on insulator (SOI) substrates.
  • the acoustic device is embedded in a gaseous, liquid, or solid environment for the emission of acoustic waves; and the reception of acoustic waves.
  • the invention provides an acoustic device comprising a flexural elastic structure which is excited to resonance by electric fields across a piezoelectric layer sub-divided into a set of parallel plate capacitors, leading to an optimal deformation of an elastic structure by the piezoelectric stress for the emission of emitting acoustic waves with the elastic structure towards an object in an adjacent medium on one side;
  • the elastic structure comprising a piezoelectric layer sub-divided into a set of parallel plate capacitors in which the application of an AC electric field causes a pattern of induced piezoelectric stress;
  • the piezoelectric parallel plate capacitors being grouped into 2 types, such that at maximum amplitude within a half-period, one type covers the area of compressive stress induced by the electric field in the piezoelectric layer, the other type covers the area of tensile stress in the piezoelectric layer;
  • the elements of the same group are poled in the same way; the elements of different groups either in the opposite direction; the two excitation signals have
  • the acoustic device further comprises extracting means configured for extracting from the signals and storing digitally for signal treatment, any one of the list comprising signal peaks, signal delays, and complete wave form; and whereby a plurality of piezoelectric elements of a micro-system is arranged in an array in order to increase the information density on the objects to be detected.
  • the invention provides a use of the acoustic devices, comprising reflecting the acoustic waves from the object in front of the elastic structure and receiving the acoustic waves on the elastic structure, whereby the reflected acoustic waves deform the elastic structure, creating electrical currents and voltages signals by a direct piezoelectric effect in the piezoelectric layer, and opening switches after each of the excitation bursts, to allow the electrical currents and voltages signals to pass to an amplifying circuit, where the signals are added or subtracted, depending on a polarization given to the two types of parallel plate electrode elements.
  • the invention provides an electronic circuit configured to drive at least a first type and a second type of piezoelectric elements of a microsystem, the first type and the second type of piezoelectric elements being configured to be part of any one or a combination of items of a list comprising a cantilever, a bridge, a diaphragm, and the piezoelectric elements being configured in a form of parallel plate electrode capacitors with an electrode system of bottom and top electrodes, whereby the first type and the second type of piezoelectric elements comprise at least a first type and a second type of electrodes, and that are adapted for a desired deformation of the at least first type and second type of piezoelectric elements, meaning that the first type of electrodes extends over a surface that exhibits a first curvature of a first sign during a maximal deflection in a given mode, and that the second type of electrodes exhibits a second curvature for a second sign during the maximal deflection at the same moment as the first one, the first type of electrodes
  • the electronic circuit further comprises a first supply line for the half-period when the first or the second piezoelectric element needs to produce tensile stress, and a second supply line for the half-period requiring compressive stress in the first or the second piezoelectric element, the first supply line being connected to the first type of electrodes, the second supply line to the second type of electrodes, in each case to one of the 2 types of electrodes called the active ones, a third supply line which is common for both the first type and the second type of piezoelectric elements, usually called "common" or ground (GND), the electric field defined between the first signal and the common in type 1 elements, and between the second signal and the common between in type 2 elements, the electronic circuit further configured such that an electric field in the second type of piezoelectric element points in opposite direction, as compared to an electric field in the first type of piezoelectric elements.
  • a third supply line which is common for both the first type and the second type of piezoelectric elements, usually called "common" or ground (
  • the electronic circuit further comprises a multitude of the described electronic circuits to drive an array of pMUT single transducers (pMUT cell), allowing also for addressing parts of the array cells, and with different phases with respect to the time in order to allow for beam steering of the emitted wave.
  • pMUT cell pMUT single transducers
  • the electronic circuit is further enabled for a sensing mode in which ultrasonic waves are intended to be detected by type 1 and type 2 elements of opposite poling directions leading to the generation of the same sign of voltage and current, wherein the electronic circuit is configured to sum up the signals from the two types for the signal production, by any one of the item in the following list: a connection of the lines by a switch that occurs when opening the receive line, a summing up of the signals after a preamplifier.
  • the electronic circuit further comprises a first supply line for the first half-period (V0), and a second supply line for the second half-period (V180°), whereby the first supply line and the second supply line are of the same polarity, being either always positive, or always negative, the first supply line is connected to the first type of piezoelectric elements, the second supply line is connected to the second type of piezoelectric elements, a third supply line which is common for the first and the second piezoelectric elements (GND), and defines an electric field between V0 to GND and V180° to GND, the signals detected by type 1 and type 2 elements having the same poling directions leading to the generation of opposite sign of voltage and current, wherein the electronic circuit is configured to measure the difference between the signals from the two types for the signal generation.
  • V0 first half-period
  • V180° the second supply line for the second half-period
  • the electronic circuit is further enabled for a sensing mode, in which ultrasonic waves are intended to be detected, wherein the electronic circuit is configured such that the generated voltage and current of the first type of electrodes have the opposite sign of the generated voltage and current if the second type of electrodes, a difference of the signals from the first type of electrode and the second type of electrode is used for signal production, after the switch opening the receive lines, whereby the signals are given to two ports of an operational amplifier, thus amplifying the difference between the two signals.
  • the invention provides a use of the method as described herein above in any one of applications of the following list: finger print detectors, flow sensors, bio-medical sensors, micropumps for fluidic elements in biomedical applications, non-destructive testing.
  • the present invention relates to piezoelectric micro-machined ultrasonic transducers (pMUT), particularly for the case of using ferroelectric thin films as piezoelectric elements. It addresses the issue of applying several elements that can be poled differently according to the local sign of curvature of the plate generating ultrasonic waves.
  • the present invention is also related to a driving circuit for supplying the elements with the necessary, time dependent voltages, and how to collect the signals generated by the same piezoelectric elements upon reception of the backscattered ultrasonic waves.
  • One difference in the present invention compared to prior art reference 9 is that in principle only one transducer is used for both functions of generating and receiving an acoustic wave.
  • One important idea of the present invention is to drive a multi-electrode device with unipolar signals distributed in time so as to create tensile stress at the correct time interval for a given vibration mode and electrode.
  • Unipolar operation allows for a higher polarization, and thus higher piezoelectric activity, and in addition, leads to a longer life time in as much as ferroelectric fatigue is excluded.
  • FIG. 7 it was described that the electromechanical response is enhanced by the application of a DC bias. For the case shown there, only one electrode was active (case CE of fig. 7b ).
  • the ideal bias amounts to about the AC signal height, giving a signal of A ( sin ( ⁇ t ) + 1), where ⁇ means the angular frequency and t the time.
  • Fig. 9b shows the situation in one of the half periods (say at phase 0°), and Fig. 9c in the other one (phase 180°).
  • Figs. 9b and 9c show an example of a device vibrating in the fundamental mode of a plate with patterned top electrodes, excited with the signals as described above.
  • the hardware of such a device is as shown in fig. 3 : figs. 9b and 9c show the deformations.
  • the device contains a plate comprising a ferroelectric thin film 903, with a first type of top electrode 901 mounted on top of the ferroelectric thin film 903, a second type of top electrode 902 also mounted on top of the ferroelectric thin film 903, and a bottom electrode 904 mounted on an opposite side of the ferroelectric thin film 903.
  • the ferroelectric thin film 903 with its electrodes is further mounted to an elastic layer 906, by means of a buffer layer 905.
  • the whole plate structure is further attached on to an outer periphery on a micromachined substrate as shown in fig. 3 .
  • the polarization directions 903a and 903b are opposite to each other.
  • the principle of the excitation of the plate is shown in fig. 9b and fig. 9c .
  • These figures illustrate RF input signals (on the left on figures 9b and 9c ) to electrodes of the plate (on the right of figures 9b and 9c ), as a function of time, referred to as solution 1 herein.
  • the plate in figures 9b and 9c is shown in a simplifier manner, i.e., without a number of the structural features represented in figure 3 , for an easier reading.
  • V + and V - have only one polarity with respect to the GND.
  • V + is given to the second type of top electrode 902, and V - to the first type of top electrode 901.
  • V + is only positive with respect to the ground.
  • the field created in the piezoelectric ferroelectric thin layer 903 has thus always the same sign for a given electrode type: for example, the polarization below the second type of electrode 902 as shown at location 903b points always "down", i.e., from the second type of top electrode to the bottom electrode 904. This downward directed polarization may be prepared by an initial poling process.
  • V - is always negative with respect to the bottom electrode 904 connected to ground potential. Its halfwave appears half a period later (180 degrees shift in the amplitude).
  • the polarization is therefore also always pointing up.
  • the polarization below the first type of electrodes 901 as shown at locations 903a points always "up", i.e., from the bottom electrode 904 towards the first type of top electrode 901.
  • the polarization in this example is pointing up below the first type of electrodes 901, i.e., also called outer electrodes herein, and pointing down below the second type of electrode 902, i.e, also called inner electrode herein.
  • the electric fields are only applied in half waves, so as the field direction is parallel to the polarization in every capacitor.
  • Figure 10 shows an alternative (referred to as solution 2 herein) using only one polarity of driving signals, e.g. only positive voltages.
  • a second signal V 180 corresponds then to a first signal V 0 that is phase shifted by 180° but else the same.
  • the film is then poled in same way at both electrode types.
  • the signals to and from inner electrodes 1002 (second type of electrode) and outer electrodes 1001 (first type of electrode) must be isolated from each other.
  • Figure 11 shows an example circuit for the realization of the positive and negative input signals, phase shifted in addition by 180°, based on a circuit of operational amplifiers simulating a threshold free diode. The circuit generates sinus curves (not shown in figure 11 ) with truncation of one polarity:
  • the electronics presented in fig. 12 is thought for using the same element for emission and detection by implementing switches to separate the emission period (connection to signal generator) from the detection period (connection to amplifier). This situation is schematically drawn in fig, 13 , showing the physical situation of the two periods.
  • a considerable enhancement of the performance of ultrasonic transducers for acoustic imaging is obtained by the use of linear of even two-dimensional arrays.
  • the diameter of the pMUT elements must be chosen near half of the wavelength in the medium through which the waves have to propagate (e.g., 80 ⁇ m in water at 10 MHz).
  • Arrays allow for a better spatial resolution (as illustrated in fig. 14 ), and also to access better to high resolution in real time.
  • the price to pay is mainly on the level of electrical contacts and electronics. For larger arrays, it becomes impossible to have the wiring on the same level as the pMUT structures.
  • the wiring problem can be overcome by attaching a connectic wafer (1402) to the so-called acoustic wafer (1401) containing the pMUT structures.
  • the signal lines are guided from the front side to the backside of the acoustic wafer through vias (1404), and then inside the connectic wafer to contacts at the periphery of the device.
  • the vias are metallized through-holes.
  • the assembly process of connectic and acoustic wafer must assure the connection of vias to the counter contacts on the connectic wafer.
  • the top electrodes are patterned for forming the piezoelectric elements of type 1 and type 2. They are connected to the vias (1508) leading across the through holes with insulation (1509) to the backside of the substrate (1507), from where the contact is made to the connectic wafer.
  • the bottom electrode is common to both elements and extends over the complete element except for the via regions, and regions outside of the active membrane for avoiding parasitic capacities.
  • emission signal bursts derived from signals Y3 and Y2 are in use (bipolar).
  • the ferroelectric layer (1503) is then poled as given in the drawing (1503a, 1503b), where also the poled regions are highlighted.
  • FIG. 16 An alternative is shown in fig. 16 .
  • the role of bottom and top electrodes are inverted.
  • the top electrode is the common one, and covers most of the element.
  • This version should be better for avoiding parasitic capacities with objects in the medium in front of the device, or pick-up of RF signals by objects in the medium (antenna effect).
  • a further variant is implemented, as an inverted Y3 signal is used, leading to a different polarization direction in one type of the piezoelectric elements (1603a) as compared to the other one (1603b).
  • a top view is shown corresponding to the acoustic wafer version of fig. 15 .
  • the active regions are below top electrodes 1703 and 1704.
  • the regions with uncovered ferroelectric layer are white, i.e., represented in non/textured surfaces.
  • the ferroelectric layer is limited to the contour 1702.
  • the grey zone 1701 corresponds to the situation of uncovered bottom electrode.
  • the black features are the contact and via lines (1705, 1706, 1707, 1708), below which there is no bottom electrode for avoiding shorts, and parasitic capacities.
  • the complete structure can be covered in addition with an insulating layer protecting from the medium (e.g. a polymer layer of parylene).
  • the most reasonable way to proceed is a line by line scan.
  • all elements of a line can be excited at the same time from one source in a parallel way, as illustrated in fig. 18 .
  • the lines 1801 and 1802 supply the RF bursts to excite the elements of line n.
  • all elements must be read-out separately in order to profit from the high resolution of the array.
  • One possibility is to dispose of one amplifier circuitry (as shown in fig. 12 ) per column.
  • Conductor lines orthogonal to the excitation lines serve to collect the signals (1804, 1805 from the two types of piezoelectric elements per cell).
  • the FET structures provide the switches to let only one cell (n,m) to the column read out lines 1804 and 1805.
  • the control line 1803 opens the switches. It is for the same line n as for the excitation signal if the back-reflected echo signal is measured.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Micromachines (AREA)
EP19172189.3A 2019-05-02 2019-05-02 Betätigung eines piezoelektrischen strukturen mit ferroelektrischer dünnschichten mit mehreren elementen Withdrawn EP3733311A1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP19172189.3A EP3733311A1 (de) 2019-05-02 2019-05-02 Betätigung eines piezoelektrischen strukturen mit ferroelektrischer dünnschichten mit mehreren elementen
PCT/IB2020/054206 WO2020222212A1 (en) 2019-05-02 2020-05-04 Actuation of piezoelectric structures with ferroelectric thin films having multiple elements

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP19172189.3A EP3733311A1 (de) 2019-05-02 2019-05-02 Betätigung eines piezoelektrischen strukturen mit ferroelektrischer dünnschichten mit mehreren elementen

Publications (1)

Publication Number Publication Date
EP3733311A1 true EP3733311A1 (de) 2020-11-04

Family

ID=66379737

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19172189.3A Withdrawn EP3733311A1 (de) 2019-05-02 2019-05-02 Betätigung eines piezoelektrischen strukturen mit ferroelektrischer dünnschichten mit mehreren elementen

Country Status (2)

Country Link
EP (1) EP3733311A1 (de)
WO (1) WO2020222212A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112986704A (zh) * 2021-02-24 2021-06-18 电子科技大学 一种基于原子力显微镜的纵向压电系数测量方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113180722A (zh) * 2021-04-20 2021-07-30 武汉大学 一种电子听诊器声学探头

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006123299A2 (en) * 2005-05-18 2006-11-23 Kolo Technologies, Inc. Methods for fabricating micro-electro-mechanical devices
WO2008054395A1 (en) * 2006-11-03 2008-05-08 Research Triangle Institute Enhanced ultrasound imaging probes using flexure mode piezoelectric transducers
US20120053393A1 (en) 2010-02-26 2012-03-01 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Sound transducer for insertion in an ear
JP2013098508A (ja) * 2011-11-07 2013-05-20 Konica Minolta Holdings Inc 圧電素子およびその製造方法と、超音波送受信プローブ
WO2016054448A1 (en) 2014-10-02 2016-04-07 Chirp Microsystems Piezoelectric micromachined ultrasonic transducers having differential transmit and receive circuitry
US20160262725A1 (en) 2015-03-10 2016-09-15 The Regents Of The University Of California Miniature ultrasonic imaging system
WO2018163963A1 (ja) * 2017-03-09 2018-09-13 京セラ株式会社 超音波センサおよび超音波センサ装置

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006123299A2 (en) * 2005-05-18 2006-11-23 Kolo Technologies, Inc. Methods for fabricating micro-electro-mechanical devices
WO2008054395A1 (en) * 2006-11-03 2008-05-08 Research Triangle Institute Enhanced ultrasound imaging probes using flexure mode piezoelectric transducers
US20120053393A1 (en) 2010-02-26 2012-03-01 Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. Sound transducer for insertion in an ear
JP2013098508A (ja) * 2011-11-07 2013-05-20 Konica Minolta Holdings Inc 圧電素子およびその製造方法と、超音波送受信プローブ
WO2016054448A1 (en) 2014-10-02 2016-04-07 Chirp Microsystems Piezoelectric micromachined ultrasonic transducers having differential transmit and receive circuitry
US20160262725A1 (en) 2015-03-10 2016-09-15 The Regents Of The University Of California Miniature ultrasonic imaging system
WO2018163963A1 (ja) * 2017-03-09 2018-09-13 京セラ株式会社 超音波センサおよび超音波センサ装置

Non-Patent Citations (19)

* Cited by examiner, † Cited by third party
Title
BELGACEM, B.CALAME, F.MURALT, P.: "IEEE Ultrasonics Symposium", vol. 922-925, 2006, IEEE, article "Thick PZT sol-gel films for pMUT transducers performances improvement"
BELGACEM, B.CALAME, F.MURALT, P.: "Piezoielectric micromachined ultrasonic transducers with thick PZT sol-gel films", J ELECTROCERAM, vol. 19, 2007, pages 369 - 373, XP019574704
DUBOIS, M.-A.MURALT, P.: "Measurement of the effective transverse piezoelectric coefficient e31,f of AIN and PZT thin films", SENS. ACTUATORS A, vol. 77, 1999, pages 106 - 112
DUBOIS, M.-A.MURALT, P.: "PZT thin film actuated elastic fin micromotor", IEEE TRANS ULTRASON. FERROELECTR. FREQ. CONTROL, vol. 45, 1998, pages 1169 - 1177, XP011437806, DOI: doi:10.1109/58.726440
FUJII, E. ET AL.: "Preparation of (001)-oriented PZT thin films and their piezoelectric applications", IEEE TRANS UFFC, vol. 54, 2007, pages 2431 - 2438
HALLER, M. I.KHURI-JAKUB, B. T.: "A surface micromachined ultrasonic air transducer", IEEE TRANS UFFC, vol. 43, 1996, pages 1 - 6, XP000557488, DOI: doi:10.1109/58.484456
KOHLI, M.MURALT, P.: "Poling of ferroelectric films", FERROELECTRICS, vol. 225, 1998, pages 155 - 162
LEDERMANN, N.MURALT, P.BABOROWSKI, J.FORSTER, M.PELLAUX, J.-P.: "Piezoelectric PZT thin film cantilver and bridge acoustic sensors for miniaturized photoacoustic gas detector", J.MICROELECTROMECH.SYSTEMS, vol. 14, 2004, pages 1650 - 1658
MAZZALAI, A.BALMA, D.CHIDAMBARAM, N.MATLOUB, R.MURALT, P.: "Characterization and fatigue of the converse piezoelectric effect in PZT films for M EMS applications", J.MEMS, vol. 24, 2015, pages 831 - 838, XP011664505, DOI: doi:10.1109/JMEMS.2014.2353855
MENG, Q.MEHREGANY, M.DENG, K.: "Modeling of the electromechanical performance of piezoelectric laminated microactuators", J.MICROMECH.MICROENG., vol. 3, 1993, pages 18 - 23, XP020069344, DOI: doi:10.1088/0960-1317/3/1/005
MURALT P ET AL: "Ferroelectric thin films for micro-sensors and actuators: a review; Ferroelectric thin films for micro-sensors and actuators", JOURNAL OF MICROMECHANICS & MICROENGINEERING, INSTITUTE OF PHYSICS PUBLISHING, BRISTOL, GB, vol. 10, no. 2, 1 June 2000 (2000-06-01), pages 136 - 146, XP020068545, ISSN: 0960-1317, DOI: 10.1088/0960-1317/10/2/307 *
MURALT, P. ET AL.: "Piezoelectric micromachined ultrasonic transducers based on PZT thin films", IEEE TRANS UFFC, vol. 52, 2005, pages 2276 - 88, XP011367560, DOI: doi:10.1109/TUFFC.2005.1563270
MURALT, P.KHOLKIN, A.KOHLI, M.MAEDER, T.: "Piezoelectric actuation of PZT thin film diaphragms at static and resonant conditions", SENS. ACTUATORS A, vol. 53, 1996, pages 397 - 403
MURALT, P: "Ferroelectric thin films for microsensors and actuators: a review", MICROMECH.MICROENG., vol. 10, 2000, pages 136 - 146, XP020068545, DOI: doi:10.1088/0960-1317/10/2/307
MURALT, P: "Piezoelectric thin films for MEMS", INTEGR. FERROELECTR., vol. 17, 1997, pages 297 - 307
MURALT, P: "Recent progress in materials issues for piezoelectric MEMS", J.AM.CERAM.SOC., vol. 91, 2008, pages 1385 - 96
PRUME, K.MURALT, P., F., C.SCHMITZ-KEMPEN, T.TIEDKE, S.: "Piezoelectric thin films: evaluation of electrical and electromechanical characteristics for MEMS devices", IEEE TRANS UFFC, vol. 54, 2007, pages 8 - 14, XP011381540, DOI: doi:10.1109/TUFFC.2007.206
SCHACHTELE, J.GOLL, E.MURALT, P.KALTENBACHER, D.: "Admittance Matrix of a Trapezoidal Piezoelectric Heterogeneous Bimorph", IEEE TRANS UFFC, vol. 59, 2012, pages 2765 - 2775
TAGANTSEV, A. K.STOLICHNOV, I.COLLA, E.SETTER, N.: "Polarization fatigue in ferroelectric films: Basic experimental findings, phenomenological scenarios, and microscopic features", J.APPL.PHYS., vol. 90, 2001, pages 1387 - 1402, XP012053917, DOI: doi:10.1063/1.1381542

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112986704A (zh) * 2021-02-24 2021-06-18 电子科技大学 一种基于原子力显微镜的纵向压电系数测量方法
CN112986704B (zh) * 2021-02-24 2022-05-03 电子科技大学 一种基于原子力显微镜的纵向压电系数测量方法

Also Published As

Publication number Publication date
WO2020222212A1 (en) 2020-11-05

Similar Documents

Publication Publication Date Title
Jung et al. Review of piezoelectric micromachined ultrasonic transducers and their applications
Muralt et al. Piezoelectric micromachined ultrasonic transducers based on PZT thin films
Muralt et al. Micromachined ultrasonic transducers and acoustic sensors based on piezoelectric thin films
US10864553B2 (en) Piezoelectric transducers and methods of making and using the same
Zhou et al. Epitaxial PMnN-PZT/Si MEMS ultrasonic rangefinder with 2 m range at 1 V drive
Wang et al. Zero-bending piezoelectric micromachined ultrasonic transducer (pMUT) with enhanced transmitting performance
Sammoura et al. Optimizing the electrode size of circular bimorph plates with different boundary conditions for maximum deflection of piezoelectric micromachined ultrasonic transducers
Sammoura et al. Theoretical modeling and equivalent electric circuit of a bimorph piezoelectric micromachined ultrasonic transducer
Wang et al. Micromachined thick film piezoelectric ultrasonic transducer array
US8770030B2 (en) Ultrasonic transmitter and receiver with compliant membrane
Wang et al. Highly sensitive piezoelectric micromachined ultrasonic transducer operated in air
CN217479067U (zh) 微机械装置及微机械系统
WO2020222212A1 (en) Actuation of piezoelectric structures with ferroelectric thin films having multiple elements
Kusano et al. Wideband air-coupled PZT piezoelectric micromachined ultrasonic transducer through DC bias tuning
US8667846B2 (en) Method of operating an ultrasonic transmitter and receiver
Pala et al. Fully transparent piezoelectric ultrasonic transducer with 3D printed substrate
Xing et al. Design, characterization, and analysis of PZT micromachined piezoelectric ultrasonic transducers with good coupling to solids
Wang et al. Micromachined ultrasonic transducers and arrays based on piezoelectric thick film
Sathishkumar Micro size ultrasonic transducer for marine applications R. Sathishkumar, A. Vimalajuliet, JS Prasath, K. Selvakumar and VHS Veer Reddy
Liu et al. Airborne Rangefinding With pMUTs Array Using Differential Structure
CN113120854B (zh) 一种背衬型高频宽带pmut单元及pmut阵列
Jung et al. Piezoelectric ultrasound MEMS transducers for fingerprint recognition
Wang et al. Broadband piezoelectric micromachined ultrasonic transducer (pMUT) using mode-merged design
Lu Piezoelectric micromachined ultrasonic transducers for fingerprint sensing
Griffin et al. Post-CMOS compatible piezoelectric micro-machined ultrasonic transducers

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN PUBLISHED

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

AX Request for extension of the european patent

Extension state: BA ME

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20210505