CN106925496A - Microelectromechanical ultrasound is popped one's head in and circuit - Google Patents

Abstract

The invention discloses a kind of microelectromechanical ultrasound probe, including silicon substrate（1）, the silicon substrate（1）Upper surface be oxide layer（2）, the oxide layer（2）Upper surface offer some cavitys（3）, some cavitys（3）In a row, row arrangement, the oxide layer（2）Upper surface bonding vibration film（4）, the vibration film（4）Upper surface set separation layer（5）, around separation layer（5）Edge and its inside offer the isolation channel of sinking（6）, the isolation channel（6）Through separation layer（5）And vibration film（4）Afterwards, its bottom land is opened in oxide layer（2）On；The separation layer（5）Upper surface on just to each cavity（3）Center position be provided with Top electrode（7）.The present invention is reasonable in design, and the structure of ultrasonic novelty, small volume, bandwidth, sensitivity are high, and noise is low, good stability.

Description

MEMS ultrasonic probe and circuit

technical field

The invention relates to the field of MEMS sensors, in particular to a micro-electromechanical ultrasonic sensor, in particular to a novel micro-electromechanical ultrasonic probe structure and circuit.

Background technique

Ultrasonic imaging technology has been widely used in many fields such as medical diagnosis, medical treatment, non-destructive testing, ultrasonic microscopy and marine landform detection. Ultrasonic transducers can emit ultrasonic waves and detect ultrasonic waves, and realize acoustic-electric conversion and electrical-acoustic conversion. They are the core components of ultrasonic imaging diagnostic equipment. The development of ultrasonic transducers plays a decisive role in improving the development of medical ultrasonic diagnostic technology and equipment. With the expansion of the application field of ultrasonic transducers, the shortcomings of traditional piezoelectric ultrasonic transducers in ultrasonic probes are gradually exposed. The most important problem is the acoustic impedance mismatch between the piezoelectric material and the working medium such as air, water and human tissue. In addition, traditional piezoelectric transducers cannot be integrated and manufactured, so the manufacturing process of linear arrays is difficult. In the past 20 years, MEMS micromachining technology has been greatly developed. A new type of micro-electromechanical ultrasonic transducer designed by using this technology not only has the advantages of broadband and high electromechanical conversion efficiency of capacitive transducers, but also makes full use of The advantages of MEMS micromachining technology are easy to make micro devices, suitable for manufacturing arrays, mass production and good matching between silicon materials and dielectric impedance.

Contents of the invention

The object of the present invention is to solve the above-mentioned problems in the prior art, and provide a novel micro-electromechanical ultrasonic probe structure and circuit, so that the ultrasonic probe can be successfully applied in medical imaging.

The present invention is achieved through the following technical solutions:

A micro-electromechanical ultrasonic probe, comprising a silicon substrate, the upper surface of the silicon substrate is an oxide layer, the upper surface of the oxide layer is provided with a number of cavities, the upper surface of the oxide layer is bonded with a vibrating film, the The upper surface of the vibrating membrane is provided with an isolation layer, and a sunken isolation groove is provided around the periphery of the isolation layer and inside, and after the isolation groove penetrates through the isolation layer and the vibration membrane, the bottom of the groove is opened on the oxide layer; An upper electrode is provided on the upper surface of the isolation layer facing the center of each cavity.

A number of cavities on the oxide layer are located in the same isolation area to form an array element; the upper surface of the isolation layer is located at the edge of an array element and a pad is provided, and two of each row in an array element Two adjacent upper electrodes and two adjacent upper electrodes in each column are connected through metal wires, and the pad is connected with the nearest upper electrode through metal wires.

Phosphorus is injected into the back of the silicon substrate, and metal sputtering is performed to form a lower electrode.

N array elements are arranged in a row to form an N array element linear array ultrasonic probe.

When working, apply a DC voltage to the upper and lower electrodes of the area array probe, and an electrostatic force will be generated between the two plates. Under the action of the electrostatic force, the vibrating film is pulled to the substrate. Alternating voltage with the same frequency will make the film vibrate continuously and realize the function of emitting ultrasonic waves. When external sound pressure acts on the vibrating film with a certain DC bias voltage, the distance of the vacuum cavity changes, the capacitance changes, and the external circuit can convert the current caused by the capacitance change into a measurable voltage signal, realizing the reception of ultrasonic waves .

The preparation method of the microelectromechanical ultrasonic probe includes the following steps:

(1), select silicon wafer and SOI wafer, and perform standard RCA cleaning;

(2) Oxidize the silicon wafer to form an oxide layer on the upper and lower surfaces;

(3) Perform photolithography on the oxide layer on the upper surface of the silicon wafer to etch a number of cavities;

(4) Carry out standard RCA cleaning and activation on the silicon wafer. After activation, the oxide layer on the upper surface of the silicon wafer is bonded to the SOI wafer at a low temperature;

(5) After bonding, use TMAH solution to etch the substrate silicon of the SOI wafer, and after cleaning, use BOE solution to etch the oxide layer on the lower surface of the silicon wafer and the oxide layer on the SOI wafer. At this time, the silicon wafer is The silicon substrate and the remaining silicon layer of the SOI wafer are the vibration film;

(6) Deposit a layer of silicon dioxide on the vibrating film as an isolation layer by LPCVD process;

(7) Sputter metal on the upper surface of the isolation layer, and form the upper electrode and pad by stripping;

(8) Isolation grooves are etched around the edges and inside of the isolation layer to form an element array, and the isolation grooves are etched out with TMAH solution. After the isolation grooves penetrate the isolation layer and the vibrating film, the bottom of the grooves is opened on the oxide layer ;

(9) Connect the upper electrodes and pads through metal leads;

(10) Phosphorus is implanted on the back of the silicon wafer to form a good ohmic contact with the silicon wafer, and metal is sputtered to form the lower electrode.

The micro-electromechanical ultrasonic transducer mentioned above can make up for the deficiency of the piezoelectric ultrasonic transducer. At the same time, the ultrasonic probe currently used in medical imaging must have a corresponding circuit to match the ultrasonic transducer, so that the ultrasonic probe can realize the function of spontaneous generation and self-reception. , to achieve medical ultrasound imaging.

Therefore, a circuit of a MEMS ultrasonic probe includes a transmitting circuit, a switching circuit and a signal conditioning circuit.

The transmitting circuit is composed of a high-voltage pulse amplifying circuit and a DC bias voltage, and simultaneously acts on the ultrasonic probe to make it emit ultrasonic waves.

The signal conditioning circuit includes a transimpedance amplification detection circuit, a filter circuit, and a low-noise amplification circuit; the transimpedance amplification detection circuit is the beginning of the signal conditioning circuit in the ultrasonic probe, which converts the weak capacitance signal into a measurable electrical signal, because the converted electrical signal The amplitude is weak, and there is noise in the circuit itself and the outside, which will reduce the signal-to-noise ratio and resolution of the output signal. The filter circuit and low-noise amplifier circuit are used to amplify and reduce the noise of the output signal to improve the signal-to-noise ratio and resolution of the system. .

A switching circuit is added between the probe and the transmitting and receiving circuits.

The MEMS ultrasonic probe needs to apply a DC bias voltage in both transmitting and receiving states, and the DC bias voltage is applied to the probe through a protection resistor. At this time, when the probe is in the transmitting state, the switch in the circuit will point to the transmitting circuit, that is, the FPGA controller and the high-voltage pulse generator. The FPGA controller controls the high-voltage pulse generator to generate high-voltage pulses and act on the probe to make the probe emit ultrasonic waves. ;When the probe is in the receiving state, the switch in the circuit will point to the receiving circuit, that is, the transimpedance amplification detection circuit and the filter circuit part. The voltage echo signal is then passed through a filter circuit to improve the signal-to-noise ratio of the voltage echo signal to achieve the effect of filtering out noise.

The present invention utilizes the ultrasonic probe prepared by the novel micro-electromechanical ultrasonic transducer. The probe not only has the advantages of wide frequency band and high electromechanical conversion efficiency of the capacitive transducer, but also makes full use of the MEMS micromachining technology, which is easy to manufacture micro-devices and is suitable for manufacturing Arrays, mass production, and good matching between silicon materials and dielectric impedance, and the use of circuits to enable the probe to realize the function of self-sensing and self-receiving, have certain application prospects in the field of ultrasound imaging.

The invention has reasonable design, and the ultrasonic probe has the advantages of novel structure, small volume, wide frequency band, high sensitivity, low noise and good stability.

Description of drawings

Fig. 1 shows the schematic diagram of the transducer N (64-1024) line array of the present invention.

Fig. 2 shows a schematic structural diagram of part A (also an array element) in Fig. 1 .

FIG. 3 shows a cross-sectional view of part B (also a cell) in FIG. 2 .

Fig. 4 is a schematic diagram of the circuit of the present invention.

Fig. 3-1 shows a schematic diagram of step 2) in the transducer manufacturing method of the present invention.

Fig. 3-2 shows a schematic diagram of step 3) in the transducer manufacturing method of the present invention.

Fig. 3-3 shows a schematic diagram of step 4) in the transducer manufacturing method of the present invention.

Figures 3-4 represent the schematic diagrams of step 5) in the transducer manufacturing method of the present invention.

3-5 show schematic diagrams of step 6) in the transducer manufacturing method of the present invention.

3-6 show schematic diagrams of step 7) in the transducer manufacturing method of the present invention.

3-7 show schematic diagrams of step 8) in the transducer manufacturing method of the present invention.

In the figure: 1 - silicon substrate, 2 - oxide layer, 3 - cavity, 4 - vibration film, 5 - isolation layer, 6 - isolation groove, 7 - upper electrode, 8 - welding pad, 9 - metal lead.

detailed description

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

A micro-electromechanical ultrasonic probe, as shown in Figure 1, consists of N (64~1024) array elements arranged in a row to form an N-element linear array ultrasonic probe.

As shown in Figure 3, it shows a cross-sectional view of a single cell in each array element, including a silicon substrate 1, the upper surface of the silicon substrate 1 is an oxide layer 2, and the upper surface of the oxide layer 2 is provided with several regular hexagons shaped cavity 3, as shown in Figure 2, several regular hexagonal cavities 3 are arranged in rows, columns or diagonally, the upper surface of the oxide layer 2 is bonded with a vibrating film 4, and the upper surface of the vibrating film 4 An isolation layer 5 is provided, and a sunken isolation groove 6 is provided around the periphery of the isolation layer 5 and its inside (the isolation groove is used to separate each element), and the isolation groove 6 runs through the isolation layer 5 and the vibrating film 4. , the bottom of the groove is opened on the oxide layer 2; the upper surface of the isolation layer 5 is provided with an upper electrode 7 (formed a patterned upper electrode) at the center of each cavity 3 . A number of cavities 3 on the oxide layer 2 are located in the same isolation area to form an array element; the upper surface of the isolation layer 5 is located at the edge of an array element and a pad 8 is provided. Two adjacent upper electrodes 7 in each row and two adjacent upper electrodes 7 in each column are connected by metal leads 9, and the pad 8 is connected to the nearest upper electrode 7 by a metal lead. 9 connected to form an array element.

The preparation method of the microelectromechanical ultrasonic probe includes the following steps:

(1) Select silicon wafers and SOI wafers, and perform standard RCA cleaning to remove various organic matter, gold dust and natural oxide layers, etc., with a resistivity of 0.01~0.08Ω.cm;

(2) Oxidize the silicon wafer to form an oxide layer on the upper and lower surfaces, as shown in Figure 3-1;

(3) Perform photolithography on the oxide layer on the upper surface of the silicon wafer to etch out several regular hexagonal cavities, as shown in Figure 3-2;

(4) Carry out standard RCA cleaning and activation on the silicon wafer. After activation, the oxide layer on the upper surface of the silicon wafer is bonded to the SOI wafer at a low temperature, as shown in Figure 3-3;

(5) After bonding, use TMAH solution to etch the substrate silicon of the SOI wafer, and after cleaning, use BOE solution to etch the oxide layer on the lower surface of the silicon wafer and the oxide layer on the SOI wafer. At this time, the silicon wafer is The silicon substrate and the remaining silicon layer of the SOI wafer are the vibration film, as shown in Figure 3-4;

(6) Deposit a silicon dioxide layer as an isolation layer on the vibrating film by LPCVD process, as shown in Figure 3-5;

(7) Sputter metal on the upper surface of the isolation layer, and use the stripping method to form the upper electrode and pad, as shown in Figure 3-6;

(8) Isolation grooves are etched around the edges and inside of the isolation layer to form an element array, and the isolation grooves are etched out with TMAH solution. After the isolation grooves penetrate the isolation layer and the vibrating film, the bottom of the grooves is opened on the oxide layer , as shown in Figure 3-7;

(9) Connect the upper electrodes and pads through metal leads;

(10) Phosphorus is implanted on the back of the silicon wafer to form a good ohmic contact with the silicon wafer, and metal is sputtered to form an integrated lower electrode (not shown in the figure).

A new MEMS ultrasonic probe circuit, as shown in Figure 4, includes a transmitting circuit, a switch (isolation) circuit and a signal conditioning circuit.

The transmitting circuit is composed of a high-voltage pulse amplifying circuit and a DC bias voltage, and acts on the ultrasonic probe at the same time to make it emit ultrasonic waves.

The signal conditioning circuit includes a transimpedance amplification detection circuit, a filter circuit, and a low-noise amplification circuit. The transimpedance amplification detection circuit is the beginning of the signal conditioning circuit in the ultrasonic probe. It converts the weak capacitance signal into a measurable electrical signal. Because the amplitude of the converted electrical signal is weak, and there is noise in the circuit itself and the outside, the signal of the output signal will The noise ratio and resolution are reduced, so the filter circuit and low-noise amplifier circuit are used to amplify and reduce the noise of the output signal to improve the system signal-to-noise ratio and resolution.

At the same time, considering that the same probe is used for transmission and reception, the high-voltage pulse signal loaded on the probe during transmission will be transmitted to the signal conditioning circuit. The amplitude of the high-voltage pulse far exceeds the maximum input voltage amplitude of the detection chip in the transimpedance amplification detection circuit. Burn out the detection chip. For this reason, a switch circuit is added between the probe and the transmitting and receiving circuits, and the high-voltage pulse signal is only applied to the transmitting state of the ultrasonic probe without affecting the receiving state of the ultrasonic probe.

In a word, the MEMS ultrasonic probe of the present invention solves the problem of acoustic impedance mismatch between the piezoelectric material and the working medium such as air, water and human tissue in the traditional piezoelectric ultrasonic probe. In addition, it also solves the problem that the piezoelectric transducer, which is the core component of the traditional piezoelectric ultrasonic probe, cannot be integrated and manufactured, and the manufacturing process of the linear array probe is difficult. The present invention includes the structural design of a single tiny vibration unit (cell), and the structure is designed as a hexagon. The working frequency of this structure is 3MHz~12MHz, which is suitable for high-frequency detection; the hexagonal cells are arranged in rows and columns to form a The array elements are arranged more closely, and the repeating units increase in a limited area, which improves the sensitivity of the sensor. N (64~1024) array elements are arranged in a row to form a line array probe; corresponding transceiver circuits are designed for the line array, and the line array is connected with the circuit to realize the detection function of the ultrasonic probe.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although detailed descriptions have been made with reference to the embodiments of the present invention, those of ordinary skill in the art should understand that the technical solutions of the present invention are modified Or equivalent replacements do not deviate from the spirit and scope of the technical solutions of the present invention, and all of them should be included in the protection scope of the claims.

Claims (5)

1. A micro-electromechanical ultrasonic probe, characterized in that: it includes a silicon substrate (1), the upper surface of the silicon substrate (1) is an oxide layer (2), and the upper surface of the oxide layer (2) is opened There are several cavities (3), the upper surface of the oxide layer (2) is bonded with a vibrating film (4), and the upper surface of the vibrating film (4) is provided with an isolation layer (5), surrounding the isolation layer (5) There are sunken isolation grooves (6) on the surrounding edges and inside, and after the isolation groove (6) penetrates the isolation layer (5) and the vibrating film (4), the bottom of the groove is opened on the oxide layer (2); An upper electrode (7) is provided on the upper surface of the isolation layer (5) facing the center of each cavity (3); Several cavities (3) on the oxide layer (2) are located in the same isolation area to form an array element; the upper surface of the isolation layer (5) is located at the edge of an array element and a pad is provided (8), two adjacent upper electrodes (7) in each row and two adjacent upper electrodes (7) in each column are connected by metal leads (9), and the pads ( 8) It is connected with the nearest upper electrode (7) through a metal lead (9); N array elements are arranged in a row to form an N array element linear array ultrasound probe. 2. The MEMS ultrasonic probe according to claim 1, wherein the value of N is 64-1024. 3. The MEMS ultrasonic probe according to claim 1 or 2, characterized in that: the shape of the cavity (3) is a regular hexagon or a circle. 4. A circuit of a micro-electromechanical ultrasonic probe, characterized in that: comprising a transmitting circuit, a switch circuit and a signal conditioning circuit; The transmitting circuit is composed of a high-voltage pulse amplifying circuit and a DC bias voltage, and simultaneously acts on the ultrasonic probe to make it emit ultrasonic waves; The signal conditioning circuit includes a transimpedance amplification detection circuit, a filter circuit, and a low-noise amplification circuit; the transimpedance amplification detection circuit is the beginning of the signal conditioning circuit in the ultrasonic probe, which converts the weak capacitance signal into a measurable electrical signal, because the converted electrical signal The amplitude is weak, and there is noise in the circuit itself and the outside, which will reduce the signal-to-noise ratio and resolution of the output signal. The filter circuit and low-noise amplifier circuit are used to amplify and reduce the noise of the output signal to improve the signal-to-noise ratio and resolution of the system. ; A switching circuit is added between the probe and the transmitting and receiving circuits. 5. A preparation method of a micro-electromechanical ultrasonic probe, characterized in that: comprising the steps of: (1), select silicon wafer and SOI wafer, and perform standard RCA cleaning; (2) Oxidize the silicon wafer to form an oxide layer on the upper and lower surfaces; (3) Perform photolithography on the oxide layer on the upper surface of the silicon wafer to etch a number of cavities; (4) Carry out standard RCA cleaning and activation on the silicon wafer. After activation, the oxide layer on the upper surface of the silicon wafer is bonded to the SOI wafer at a low temperature; (5) After bonding, use TMAH solution to etch the substrate silicon of the SOI wafer, and after cleaning, use BOE solution to etch the oxide layer on the lower surface of the silicon wafer and the oxide layer on the SOI wafer. At this time, the silicon wafer is The silicon substrate and the remaining silicon layer of the SOI wafer are the vibration film; (6) Deposit a layer of silicon dioxide on the vibrating film as an isolation layer by LPCVD process; (7) Sputter metal on the upper surface of the isolation layer, and form the upper electrode and pad by stripping; (8) Isolation grooves are etched around the edges and inside of the isolation layer to form an element array, and the isolation grooves are etched out with TMAH solution. After the isolation grooves penetrate the isolation layer and the vibrating film, the bottom of the grooves is opened on the oxide layer ; (9) Connect the upper electrodes and pads through metal leads; (10) Phosphorus is implanted on the back of the silicon wafer to form a good ohmic contact with the silicon wafer, and metal is sputtered to form the lower electrode.