CN117019606A - Self-focusing capacitive micro-mechanical ultrasonic sensor device and preparation method thereof - Google Patents

Abstract

The invention discloses a self-focusing capacitive micro-mechanical ultrasonic sensor device and a preparation method thereof, which are applied to the field of capacitive micro-Mechanical Ultrasonic Sensors (CMUTs) and aim at solving the problems that the prior ultrasonic focusing technology has complex peripheral circuit and non-adjustable focusing focus; according to the invention, the control components are added to one or more CMUT units in the array element, and the control components are used for controlling the CMUT units or the CMUT films in the array element to rotate in proper directions so as to perform focus control; the device of the invention does not need complex peripheral circuits; and the focal point of the focus is adjustable.

Description

Self-focusing capacitive micro-mechanical ultrasonic sensor device and preparation method thereof

Technical Field

The invention belongs to the field of capacitive micro-Mechanical Ultrasonic Sensors (CMUTs), and particularly relates to a structure, a processing method, materials and the like of the CMUT.

Background

Capacitive Micro-machined Ultrasonic Transducers (CMUT) is an ultrasonic transmitting and receiving device fabricated using MEMS technology, and the CMUT sensor is structurally characterized in that the CMUT basic structure comprises a substrate (typically silicon with high doping concentration and thus can be used as a bottom electrode), a cavity, a supporting wall, a membrane and a top electrode on the membrane and thus can be considered as a capacitor. As shown in the cross-sectional view of the individual devices of fig. 1. The vibrating film is driven by electrostatic force generated by voltage applied to the top electrode and the bottom electrode to generate vibration, and ultrasonic waves are emitted; the ultrasonic wave can be received by generating capacitance change between the top electrode and the bottom electrode by being excited by external ultrasonic wave. Compared with the traditional piezoelectric sensor, the CMUT sensor has the advantages of large bandwidth, easiness in integration with an integrated circuit and the like, and has good application prospect. Especially, the release of the palm ultrasonic Butterfly IQ in 2018 proves that the CMUT has great potential in the field of medical imaging.

Fig. 1 is a cross-sectional view of a conventional CMUT device. Comprises a top electrode, a bottom electrode, a cavity, a vibrating film, an insulating layer, a supporting wall and the like.

Ultrasonic focusing can improve the sound pressure of ultrasonic waves and the penetrating power of the ultrasonic waves. CMUT achieves ultrasonic focusing function under existing manufacturing process, the first mode is achieved by delay control circuit of different emission pulses of different array elements (elements) (e.g. "i.o. wygant et al", "An integrated circuit with transmit beamforming flip-chip bonded to A2-D CMUT array for 3-D ultrasound imaging", "in IEEE Transactions on Ultrasonics, ferroelectronics, and Frequency Control, vol.56, no.10, pp.2145-2156,October 2009", "a.stuart savonia et al", "a256-Element Spiral CMUT Array with Integrated Analog Front End and Transmit Beamforming Circuits", "2018IEEE International Ultrasonics Symposium (IUS), kobe, japan,2018, pp.206-212"), and the second mode is focusing by fixing different array elements on one focusing plane (e.g. "CN109499866U", "CN107670183 a") or using ultrasonic space emission characteristics (e.g. "CN 111250376B").

In the first way, a relatively complex peripheral circuit is required to work normally, which also results in a relatively complex overall ultrasound system; in the second way, the focal point of the focus is not adjustable, limited by the fixed plane.

Disclosure of Invention

In order to solve the technical problems, the invention provides a self-focusing capacitive micro-mechanical ultrasonic sensor device and a preparation method thereof, wherein one or more CMUT units in an array element are added with control components, and the control components are used for controlling the rotation of a single or a plurality of CMUT units or CMUT films in the array element to rotate in a proper direction so as to perform focusing control; the peripheral circuit is simpler, and the focusing focus is adjustable.

One of the technical schemes adopted by the invention is as follows: a self-focusing capacitive micro-mechanical ultrasonic sensor device comprising a plurality of array elements, each array element comprising a plurality of self-focusing capacitive micro-mechanical ultrasonic sensors, each self-focusing capacitive micro-mechanical ultrasonic sensor comprising: a bottom electrode, a top electrode, an insulating layer, a cavity, a supporting wall and a vibrating film;

the insulating layer is arranged on the upper surface of the bottom electrode;

the shape of the vibrating film is matched with that of the cavity, and the cavity is arranged between the vibrating film and the insulating layer; the support wall being disposed around an edge of the cavity; the top electrode is arranged on the vibrating film;

top electrodes of the self-focusing capacitive micro-mechanical ultrasonic sensors in the array element are connected in parallel;

the vibrating film is controlled to control the rotation direction based on electrostatic mode; specific: the one or more self-focusing capacitive micro-mechanical ultrasonic sensors in the array element further comprise a control electrode arranged on the vibrating film; the control electrode is connected with the external electrode.

The second technical scheme adopted by the invention is as follows: a method of fabricating a self-focusing capacitive micromachined ultrasonic sensor device, comprising:

s1, growing a layer of silicon oxide and a layer of silicon nitride on a highly doped silicon wafer substrate to serve as an insulating layer;

s2, depositing polysilicon on the upper surface of the insulating layer to prepare a sacrificial layer; the sacrificial layer comprises a circular body and a plurality of release channels connected with the circular body;

s3, depositing a silicon nitride film on the sacrificial layer; simultaneously generating a support wall;

s4, opening corrosion holes at the opening positions of the release channels, and releasing the sacrificial layer to form a cavity;

s5, sealing the corrosion hole after the sacrificial layer is released;

s6, performing thinning operation to restore the film thickness;

s7, depositing a metal layer on the upper surface of the film, wherein the metal layer comprises the following components: top electrode and control electrode.

The invention has the beneficial effects that: according to the invention, the control components are added to one or more CMUT units in the array element, and the control components are used for controlling the CMUT units or the CMUT films in the array element to rotate in proper directions so as to perform focus control; because these control components are placed directly above the CMUT cells or array elements, complex peripheral circuitry is not required; on the other hand, the control intensity externally connected with the control components can be adjusted, so that the focusing focus can be changed; the invention has the following advantages:

1. the CMUT unit and the array element control method provided by the invention can enable the CMUT unit and the array element to rotate in a hope mode, thereby achieving the purpose of ultrasonic focusing. Left side add electrode: the thin film is tilted and focused to the left, and the tilt angles of different voltages are different. Right side add electrode: the thin film is inclined and focused to the right, and the inclination angles of different voltages are different. Two sides are added with electrodes: the amount of tilting can be finely adjusted by utilizing the force difference generated by the voltage difference between the two sides.

2. The CMUT unit and the array element device provided by the invention have the advantages that a complex peripheral integrated circuit mode is omitted in a driving mode, the focusing point can be controlled according to the requirement, and the focusing flexibility is increased.

Drawings

Fig. 1 is a cross-sectional view of a conventional CMUT device;

fig. 2 is a top view comparison of a conventional CMUT device with the CMUT device of the present invention;

wherein, (a) is a top view of an existing CMUT device, and (b) is a top view of the CMUT device of the invention;

fig. 3 is a comparison of the connection modes of the conventional array element and each CMUT device in the array element of the present invention;

wherein, (a) is the connection mode of the CMUT device in the prior array element, and (b) is the connection mode of the CMUT device in the array element;

fig. 4 is a main component illustration of a conventional CMUT device and a CMUT device of the present invention;

FIG. 5 is a schematic diagram of the left and right side additional electrodes of the CMUT device in the array element of the present invention;

FIG. 6 is a simplified acoustic focusing diagram;

fig. 7 is a diagram of CMUT array elements for simplifying the number of devices;

FIG. 8 is one implementation of the present invention with control electrodes on both sides;

fig. 9 is a cross-sectional view of a single CMUT device of the invention;

FIG. 10 illustrates a device fabrication method of the present invention using electrostatic focusing control;

wherein, (a) is an insulating layer generation schematic diagram, (b) is a sacrificial layer generation schematic diagram, (c) is a silicon nitride film generation schematic diagram, (d) is a cavity generation schematic diagram, (e) is a seal corrosion hole schematic diagram, and (f) is a metal layer generation schematic diagram.

Detailed Description

The present invention will be further explained below with reference to the drawings in order to facilitate understanding of technical contents of the present invention to those skilled in the art.

The invention performs focusing control by adding control components to one or more CMUT units in an array element, and controlling the CMUT units or CMUT membranes in the array element to rotate in proper directions by the control components. Since these control components are placed directly on top of the CMUT cells or array elements, the complex peripheral circuitry required in the prior art first preparation approach described above is avoided. On the other hand, the control intensity externally connected with the control components can be adjusted, so that the focusing focus can be changed, and the condition of fixed focus in the second mode existing in the prior art can be avoided.

The array element is composed of a plurality of CMUT units, and each CMUT unit is provided with a control component, namely the array element is provided with the control component.

These control means may be controlled electrostatically, electrically, electromagnetically, or the like. The electric heating mode specifically comprises the following steps: the one or more self-focusing capacitive micro-mechanical ultrasonic sensors in the array element further comprise a heating deformation material layer arranged on the vibrating film; the electromagnetic mode is specifically as follows: the one or more self-focusing capacitive micro-mechanical ultrasonic sensors in the array element further comprise a magnetic material disposed on the vibrating membrane.

The present embodiment will be described by taking an electrostatic control method as an example.

As shown in fig. 2 (a), a simplified top view of a conventional device includes a thin film (dotted line portion) and a top electrode (solid line portion). A simple top view of a single device, for example electrostatically controlled, is shown in fig. 2 (b), with control components in addition to the membrane and top electrode.

In fig. 2, a dotted circle represents a device vibration film, and a solid circle represents an upper electrode, taking electrostatic control as an example. The two sided shuttle shape of fig. 2 (b) represents a new added control electrode of the present invention, which may be present simultaneously or placed one on top of the other for different applications. The device can focus to the left side through the left electrode, and the focusing angle and depth are different through applying voltages with different magnitudes; the device can be focused to the right side through the right electrode, and the focusing angle and depth are different through applying voltages with different magnitudes; the two sides exist at the same time, and the focusing angle and depth can be accurately adjusted by adjusting the voltage difference of the two sides.

Those skilled in the art should appreciate that the placement of the upper electrode and the control electrode on the upper and lower surfaces of the vibrating membrane does not affect the function.

For the CMUT devices, when in operation, a plurality of devices are generally connected in parallel to form an array element, and the existing array element generally adopts the connection mode in fig. 3 (a), namely, the top electrodes of the CMUT devices in the array element are connected in parallel; the invention adopts the connection mode in the figure 3 (b), and adds the electrodes on the left side and the right side and electrode connection lines; specifically, besides the parallel connection of the top electrodes of the CMUT devices in the array element, the focusing control of the same array element also comprises the parallel connection of the control electrodes on the same side of the top electrodes of the CMUT devices in the array element.

The common CMUT manufacturing method is to manufacture CMUT units and array elements with fixed membranes by a sacrificial layer release method or a bonding method, and the devices generate ultrasonic waves or receive ultrasonic waves through up-and-down vibration of the membranes.

The invention can control partial CMUT units or array elements to deflect in a preset mode by controlling the electrode structure of the CMUT unit membrane or the CMUT array element structure, thereby achieving the purpose of ultrasonic focusing without adding a complex peripheral control circuit.

The deflection of an array element is known to those skilled in the art as a specific deflection of all CMUT cells in the array element and a consistent deflection state or direction.

FIG. 4 is a schematic diagram of the main components of a prior art device and a device of the present invention; in fig. 4, a dotted circle represents the device vibration film, and a solid circle represents the upper electrode. The two sided fusiform represents the newly added control electrode of the present invention.

FIG. 5 shows the device of the present invention with electrodes added to the left and right sides to control the deflection of the device to the left and right, respectively; wherein the square represents an external electrode; the circles in fig. 5 represent individual devices, with the left and right vertical lines of circles representing the added left and right electrodes, all of which are connected together.

Fig. 6 shows a simplified acoustic focusing diagram. Applying voltage to the right electrode of a device or array element, and converging ultrasonic waves to the right; and applying voltage to the left electrode of one device or array element, and converging ultrasonic waves to the left.

Fig. 7 is a diagram of CMUT array elements for simplifying the number of devices in the implementation of the CMUT device with a control electrode on one side of the device.

Wherein the top square is the top electrode external electrode, and the bottom square is the bottom electrode external electrode; the other part of the strip is a connecting wire; the dashed circle is the circular diaphragm of the CMUT; the solid circle is the top electrode of the device; the bottom electrode of the device is a highly doped silicon substrate.

The left side shuttle shape and the right side shuttle shape are used for controlling the left or right deflection of the vibrating film so as to achieve the purpose of self-focusing. The left control electrode connection and the right control electrode connection are used to connect shuttle-shaped portion electrodes in a plurality of devices in parallel.

One implementation of a control electrode on both sides is shown in fig. 8. Fig. 8 is a diagram of CMUT array elements for simplifying the number of devices. Wherein the top square is the top electrode external electrode, and the bottom square is the bottom electrode external electrode; the other part of the strip is a connecting wire; the dashed circle is the circular diaphragm of the CMUT; the solid circle is the top electrode of the device; the bottom electrode of the device is a highly doped silicon substrate. The control electrode parts at the left and right sides are respectively controlled by different external electrodes. The electrode connection method is not limited to the method shown in fig. 8.

A cross-sectional view of a single CMUT device is shown in fig. 9 (a circular vibrating membrane is exemplified).

A bottom electrode (silicon substrate) 100 is included from bottom to top; a first insulating layer of silicon oxide 200, a second insulating layer of silicon nitride 210; a cavity 300; a support wall left side 400 and right side 410; a vibrating membrane 500; top electrode 600 and left and right electrodes 610,620.

The present invention controls the manner in which CMUT devices or array elements focus, including but not limited to the following:

1. the CMUT devices in the same array element are independently controlled; the CMUT device is controlled independently, namely an external electrode is needed to be arranged corresponding to a single device; the different CMUT devices that are individually controlled are no longer connected in parallel, corresponding to each device being independent.

2. The CMUT devices in different areas in the same array element are respectively controlled;

3. and uniformly controlling the same array element.

The present invention controls CMUT devices or array elements, including but not limited to the following:

1. controlling an electrostatic mode;

2. controlling an electric heating mode;

3. electromagnetic control.

One way of preparation controlled electrostatically is shown in fig. 10:

in the first step, a layer of silicon oxide 200 and a layer of silicon nitride 210 are grown on a highly doped silicon substrate 100 as insulating layers, resulting in the structure shown in fig. 10 (a).

Second, a sacrificial layer of polysilicon 350 is deposited over the insulating layer 210 and then patterned to produce the cavity 300 after subsequent removal of the sacrificial layer, resulting in the structure shown in fig. 10 (b).

Third, depositing a silicon nitride film 500 on the sacrificial layer 350; support walls 400 and 410 are also created resulting in the structure shown in fig. 10 (c).

Fourth, after the silicon nitride film is deposited, etching holes 700 and 710 are formed beside the silicon nitride film, the etching holes are connected with the etching channel, the other end of the etching channel is connected with the sacrificial layer, and the etching liquid can etch the material in the etching channel and the sacrificial layer completely through the etching holes, so that a cavity as shown in fig. 10 (d) is formed in the part of the original sacrificial layer, and the process is called sacrificial layer release. The etching solution is typically a KOH solution.

The cavity may also be circular, square, hexagonal, etc.

Fifthly, after the release of the sacrificial layer is finished, in order to enable the device to be used in liquid, the corrosion hole needs to be sealed; the etching holes can be sealed by PECVD; the thickness of silicon nitride on the whole silicon wafer is increased while the corrosion hole is sealed, and the thickness of the film is also increased, so that thinning is required to restore the thickness of the film, and the structure shown in fig. 10 (e) is obtained.

And sixthly, performing metal sputtering and patterning on the basis of reducing the thickness of the thin film to form a top electrode, left and right control electrodes and all electrode connecting lines, thereby obtaining the structure shown in fig. 10 (f).

By adopting electrothermal control, a movable component, generally two layers of different materials, is added to a CMUT device or array element of a part to be controlled, and the materials generate heat to deform after being electrified, so that position change is generated.

By adopting electromagnetic control, an external magnetic material and an external magnetic field are needed, and force is generated through magnetic field change or current change in the magnetic material, so that position change is caused.

Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims (6)

1. A self-focusing capacitive micro-mechanical ultrasonic sensor device comprising a plurality of array elements, each array element comprising a plurality of self-focusing capacitive micro-mechanical ultrasonic sensors, each self-focusing capacitive micro-mechanical ultrasonic sensor comprising: a bottom electrode, a top electrode, an insulating layer, a cavity, a supporting wall and a vibrating film;

the insulating layer is arranged on the upper surface of the bottom electrode;

the shape of the vibrating film is matched with that of the cavity, and the cavity is arranged between the vibrating film and the insulating layer; the support wall being disposed around an edge of the cavity; the top electrode is arranged on the vibrating film;

top electrodes of the self-focusing capacitive micro-mechanical ultrasonic sensors in the array element are connected in parallel;

the vibrating film is controlled to control the vibrating direction based on electrostatic mode control; specific: the one or more self-focusing capacitive micro-mechanical ultrasonic sensors in the array element further comprise a control electrode arranged on the vibrating film; the control electrode is connected with the external electrode.

2. A self-focusing capacitive micro-mechanical ultrasonic sensor device according to claim 1, wherein each self-focusing capacitive micro-mechanical ultrasonic sensor in the same array element corresponds to a separate external electrode; the control electrodes of the focusing capacitive micro-mechanical ultrasonic sensors are connected with the corresponding independent external electrodes.

3. The self-focusing capacitive micro-mechanical ultrasonic sensor device of claim 1, wherein the same array element comprises a plurality of regions, each region corresponding to an independent external electrode; the control electrodes of all the self-focusing capacitive micro-mechanical ultrasonic sensors in each area are connected in parallel and then connected with the independent external electrodes corresponding to the area.

4. The self-focusing capacitive micro-mechanical ultrasonic sensor device of claim 1, wherein the same array element corresponds to an independent external electrode; all control electrodes of the self-focusing capacitive micro-mechanical ultrasonic sensors in the same array element are connected in parallel and then connected with independent external electrodes corresponding to the area.

5. A self-focusing capacitive micro-mechanical ultrasonic sensor device according to any one of claims 2-4, characterized in that the vibration direction of the vibration film of the self-focusing capacitive micro-mechanical ultrasonic sensor is controlled by adjusting the voltage level of the external electrode.

6. A method of fabricating a self-focusing capacitive micromachined ultrasonic transducer device, comprising:

s1, growing a layer of silicon oxide and a layer of silicon nitride on a highly doped silicon wafer substrate to serve as an insulating layer;

s2, depositing polysilicon on the upper surface of the insulating layer to prepare a sacrificial layer; the sacrificial layer comprises a circular body and a plurality of release channels connected with the circular body;

s3, depositing a silicon nitride film on the sacrificial layer; simultaneously generating a support wall;

s4, opening corrosion holes at the opening positions of the release channels, and releasing the sacrificial layer to form a cavity;

s5, sealing the corrosion hole after the sacrificial layer is released;

s6, performing thinning operation to restore the film thickness;

s7, depositing a metal layer on the upper surface of the film treated in the step S6, wherein the metal layer comprises the following components: top electrode and control electrode.