A high-performance micromechanical ultrasonic transducer

Abstract

This invention discloses a high-performance micromechanical ultrasonic transducer, comprising a substrate and a diaphragm attached to the top of the substrate; a cavity is provided in the central region of the substrate, and the diaphragm forms several cantilever beams through the cavity, with air slits provided between adjacent cantilever beams; one end of each cantilever beam near the central region of the substrate is a pointed tip, and a through-hole region is provided at the tip of the cantilever beam, with several rows of through holes provided within the through-hole region. The high-performance micromechanical ultrasonic transducer provided by this invention has the advantages of large bandwidth, low quality factor, and stress insensitivity, and can be used in ultrasonic sensing applications such as distance monitoring and gesture recognition.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical technology, and in particular to a high-performance micromechanical ultrasonic transducer. Background Technology

[0002] A piezoelectric micromachined ultrasonic transducer (PMUT) is an ultrasonic transducer fabricated using MEMS (Micro-electro-mechanical Systems) technology and operating based on the piezoelectric or inverse piezoelectric effect mechanism. It can transmit and receive ultrasonic waves. Due to its advantages such as small size, low power consumption, and mass production capability, piezoelectric micromachined ultrasonic transducers are widely used in the field of ultrasonic sensing.

[0003] In ultrasonic sensing applications, the minimum detection distance and axial resolution of micromechanical ultrasonic transducers depend on their bandwidth and quality factor parameters. However, existing micromechanical ultrasonic transducers often suffer from narrow bandwidth and high quality factor, thus limiting their detection accuracy and range. Summary of the Invention

[0004] The purpose of this invention is to provide a high-performance micromechanical ultrasonic transducer to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides a high-performance micromechanical ultrasonic transducer, comprising a substrate and a diaphragm attached to the top of the substrate; a cavity is provided in the central region of the substrate, and the diaphragm forms a plurality of cantilever beams through the cavity, with an air slit provided between two adjacent cantilever beams; one end of the cantilever beam near the central region of the substrate is a pointed tip, and a through-hole region is provided at the pointed tip of the cantilever beam, with a plurality of rows of through holes provided in the through-hole region.

[0006] Preferably, the diaphragm is constructed from a piezoelectric monocrystalline structure or a piezoelectric bicrystalline structure.

[0007] Preferably, the piezoelectric single-crystal structure includes a top electrode layer, a piezoelectric layer, a bottom electrode layer, and a support layer arranged sequentially from top to bottom; the via region is composed of a single layer of material, which is the support layer.

[0008] Preferably, the piezoelectric bicrystalline structure includes a top electrode layer, an upper piezoelectric layer, an intermediate electrode layer, a lower piezoelectric layer, and a bottom electrode layer arranged sequentially from top to bottom; the via region is composed of a single layer of material, which is the lower piezoelectric layer.

[0009] Preferably, the diaphragm has a polygonal or circular shape.

[0010] Compared with the prior art, the present invention has the following advantages and technical effects:

[0011] The provided ultrasonic transducer design has the advantages of large bandwidth and low Q value. The removal of material in the middle region of the diaphragm and the design of the through-hole structure reduce the diaphragm mass and increase the thermoviscous damping, which in turn leads to an increase in PMUT bandwidth and a decrease in Q value. In ultrasonic sensing applications, the provided ultrasonic transducer has higher sensing accuracy and a smaller detection blind zone. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 Figure (a) is a top view and Figure (b) is a cross-sectional view of the MEMS ultrasonic transducer according to Embodiment 1 of the present invention.

[0014] Figure 2 This is a schematic diagram of the through-hole structure according to Embodiment 1 of the present invention;

[0015] Figure 3 Figure (a) is a top view and Figure (b) is a cross-sectional view of the MEMS ultrasonic transducer according to Embodiment 2 of the present invention.

[0016] Figure 4 Figure (a) is a top view and Figure (b) is a cross-sectional view of the MEMS ultrasonic transducer according to Embodiment 3 of the present invention.

[0017] Figure 5 This is a comparison chart of the sound pressure spectrum curves of Embodiment 1 of the present invention and PMUT based on piezoelectric single-crystal stack and traditional cantilever beam structure;

[0018] Figure 6 This is a comparison chart of the sound pressure spectrum curves of Embodiment 2 of the present invention and PMUT based on piezoelectric single-crystal stack and traditional cantilever beam structure;

[0019] Figure 7 This is a comparison chart of the sound pressure spectrum curves of Embodiment 3 of the present invention and the PMUT based on piezoelectric dual-crystal stack and traditional cantilever beam structure;

[0020] In the figure: In Example 1, 100-MEMS ultrasonic transducer, 101-cantilever beam, 102-through hole area, 103-through hole, 104-air slit, 105-metal pad, 106-top electrode, 107-upper piezoelectric layer, 108-middle electrode, 109-lower piezoelectric layer, 110-bottom electrode, 111-substrate, 112-cavity;

[0021] In Example 2, 200 is a MEMS ultrasonic transducer, 201 is a cantilever beam, 202 is a through-hole area, 203 is a through-hole, 204 is an air slit, 205 is a metal pad, 206 is a top electrode, 207 is a piezoelectric layer, 208 is a bottom electrode, 209 is a support layer, 210 is a substrate, and 211 is a cavity.

[0022] In Example 3, 300 is a MEMS ultrasonic transducer, 301 is a cantilever beam, 302 is a through-hole area, 303 is a through-hole, 304 is an air slit, 305 is a metal pad, 306 is a top electrode, 307 is a piezoelectric layer, 308 is a bottom electrode, 309 is a support layer, 310 is a substrate, and 311 is a cavity. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] This invention provides a high-performance micromechanical ultrasonic transducer, a substrate, and a diaphragm. The substrate includes a base, and the diaphragm is attached to the top of the base. A cavity is provided in the central region of the base, and the diaphragm forms several cantilever beams through the cavity. An air slit is provided between two adjacent cantilever beams. The peripheral region of the diaphragm contains a multilayer piezoelectric stacked material, which constitutes the driving region of the diaphragm. In the middle region of the diaphragm, only a single layer of material is retained. The end of the cantilever beam near the central region of the base is pointed, and a multi-row through-hole structure is formed on the pointed end of the cantilever beam.

[0025] The diaphragm material stack can be either a piezoelectric single-crystal structure or a piezoelectric bicrystalline structure. When the diaphragm adopts a piezoelectric single-crystal structure, only the support layer material is retained in the middle region of the diaphragm, and the remaining material is removed by patterning during the fabrication process. When the diaphragm adopts a piezoelectric bicrystalline structure, only the lower piezoelectric layer material is retained in the middle region of the diaphragm, and the remaining material is removed by patterning during the fabrication process.

[0026] The number of rows, diameter, and spacing of through holes in the tip region of the cantilever beam are not limited. However, a smaller through hole spacing results in a larger bandwidth and a lower quality factor for the ultrasonic transducer, and this parameter is limited by manufacturing capabilities. The through hole diameter and number of rows are related to the operating frequency of the ultrasonic transducer and affect its thermoviscous damping. The selection of these parameters will affect the final performance of the ultrasonic transducer, and optimal choices must be made based on actual needs.

[0027] To avoid asynchronous vibration caused by uneven process, a connecting beam structure can be introduced between cantilever beams to form a rigid mechanical connection, or a soft mechanical connection can be formed by sealing the slits with flexible materials.

[0028] The geometry of the diaphragm is not limited and can be any polygon or circle. Regardless of the diaphragm's geometry, the through-hole design of this invention can achieve the goal of reducing the quality factor and increasing the bandwidth.

[0029] Example 1

[0030] This embodiment provides a MEMS ultrasonic transducer, such as Figure 1 As shown, the MEMS ultrasonic transducer 100 includes a substrate 111 and a diaphragm. A cavity 112 is provided in the central region of the substrate 111, and the cavity 112 is located below the diaphragm. The diaphragm is a piezoelectric bicrystalline structure with a square shape and is attached to the substrate 111. The diaphragm is composed of multiple cantilever beams 101, and its peripheral region is provided with a top electrode 106, an upper piezoelectric layer 107, a middle electrode 108, a lower piezoelectric layer 109, and a bottom electrode 110 for applying electrical signals and providing driving capability. In the middle region of the diaphragm, i.e., the through-hole region 102 of the cantilever beam 101, only the lower piezoelectric layer 109 is retained, and the other layers are removed, and eight rows of through holes 103 are formed on the lower piezoelectric layer 109.

[0031] The top electrode 106 of the MEMS ultrasonic transducer 100 is connected to the bottom electrode 110, and the two electrodes, along with the intermediate electrode 108, are connected to two metal pads 105 respectively.

[0032] like Figure 2 As shown, a through hole 103 is formed on the through hole region 102 at the tip of the cantilever beam 101 and penetrates the lower piezoelectric layer 109, allowing air to communicate between the front and back of the cantilever beam 101; an air slit 104 is located between the two cantilever beams 101.

[0033] like Figure 5 As shown, the acoustic pressure sensitivity of Example 1 and the traditional cantilever beam PMUT are compared through finite element simulation. Example 1 and the traditional cantilever beam PMUT have the same membrane layer configuration, membrane layer thickness and similar resonant frequency. In comparison, Example 1 has a larger bandwidth.

[0034] Example 2

[0035] This embodiment provides a MEMS ultrasonic transducer, such as Figure 3 As shown, the MEMS ultrasonic transducer 200 includes a substrate 210 and a diaphragm. A cavity 211 is provided in the central region of the substrate 210, and the cavity 211 is located below the diaphragm. The diaphragm is a piezoelectric single crystal structure with a square shape and is attached to the substrate 210. The diaphragm is composed of multiple cantilever beams 201. An air slit 204 is located between two cantilever beams 201. A top electrode 206, a piezoelectric layer 207, a bottom electrode 208, and a support layer 209 are provided in the outer region of the cantilever beams 201 for applying electrical signals and providing driving capability. In the middle region of the diaphragm, i.e., the through-hole region 202 of the cantilever beams 201, only the support layer 209 is retained, and the other layers are removed. Ten rows of through holes 203 are formed on the support layer 209.

[0036] The top electrode 206 and bottom electrode 208 of the MEMS ultrasonic transducer 200 are connected to two metal pads 205 respectively.

[0037] like Figure 6 As shown, the sound pressure sensitivity of Example 2 and the traditional cantilever beam PMUT are compared through finite element simulation. Example 2 and the traditional cantilever beam PMUT have the same membrane layer configuration, membrane layer thickness and similar resonant frequency. In comparison, Example 2 has a larger bandwidth.

[0038] Example 3

[0039] This embodiment provides a MEMS ultrasonic transducer, such as Figure 4 As shown, the MEMS ultrasonic transducer 300 includes a substrate 310 and a diaphragm. A cavity 311 is provided in the central region of the substrate 310, and the cavity 311 is located below the diaphragm. The diaphragm is a piezoelectric single crystal structure with a circular shape and is attached to the substrate 310. The diaphragm is composed of multiple cantilever beams 301, and an air slit 304 is located between two cantilever beams 301. A top electrode 306, a piezoelectric layer 307, a bottom electrode 308, and a support layer 309 are provided in the peripheral region of the cantilever beams 301 for applying electrical signals and providing driving capability. In the middle region of the diaphragm, i.e., the through-hole region 302 of the cantilever beams 301, only the support layer 309 is retained, and the other layers are removed, and 10 rows of through holes 303 are formed on the support layer 309.

[0040] The top electrode 306 and bottom electrode 308 of the MEMS ultrasonic transducer 300 are connected to two metal pads 305 respectively.

[0041] like Figure 7As shown, the sound pressure sensitivity of Example 1 and the traditional cantilever beam PMUT obtained through finite element simulation is compared. Among them, Example 3 has the same membrane layer setting, membrane layer thickness and similar resonant frequency as the traditional cantilever beam PMUT. In comparison, Example 3 has a larger bandwidth.

[0042] The high-performance micromechanical ultrasonic transducer provided by this invention is summarized in Table 1, based on the performance parameters of Embodiment 1, Embodiment 2, Embodiment 3 obtained from finite element simulation, as well as the corresponding traditional cantilever beam structure PMUT for each embodiment.

[0043] Table 1: Summary of Performance Parameters of PMUT in Examples 1, 2, and 3 and Traditional Cantilever Beam Structure

[0044]

[0045] Where Q is the quality factor; FBW is the fractional bandwidth, defined as 1 / Q × 100%; FOM is the performance index, defined as sound pressure sensitivity divided by the quality factor, and the performance parameters are from... Figure 5 , Figure 6 and Figure 7 Extracted from the provided sound pressure sensitivity curve. Compared with the traditional cantilever beam structure PMUT, Examples 1, 2, and 3 all have lower quality factors, larger bandwidth, and better overall performance, solving the problems of narrow bandwidth, high Q value, and high stress sensitivity of the existing PMUT.

[0046] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A high-performance micromechanical ultrasonic transducer, characterized in that, The device includes a substrate and a diaphragm attached to the top of the substrate; a cavity is provided in the central region of the substrate, and the diaphragm forms several cantilever beams through the cavity, with an air slit between two adjacent cantilever beams; one end of each cantilever beam near the central region of the substrate is a pointed tip, and a through-hole region is provided at the pointed tip of the cantilever beam, with several rows of through holes provided in the through-hole region; The diaphragm is a piezoelectric bicrystalline structure. The piezoelectric bicrystalline structure includes, from top to bottom, a top electrode layer, an upper piezoelectric layer, a middle electrode layer, a lower piezoelectric layer, and a bottom electrode layer. The via region is composed of only a single layer of material, which is the lower piezoelectric layer, and the plurality of vias penetrate the lower piezoelectric layer.

2. The high-performance micromechanical ultrasonic transducer according to claim 1, characterized in that, The diaphragm has a polygonal or circular shape.

Images