CN101477083B - Thin film sonic sensor and method with active acoustic energy loss inhibition function - Google Patents

Abstract

The invention provides a method for improving the sensitivity of thin-film bulk acoustic wave (BAW) sensors by utilizing an active control technique, and a thin-film BAW sensor stricture for realizing the method. The method comprises the following steps that: an active control piezoelectric layer and a corresponding metal electrode are arranged between the underside of a sensitive piezoelectric layer of a conventional thin-film BAW resonator or sensor and a substrate; while an electrical signal needs to be applied to the sensitive piezoelectric layer during detection, an electrical signal is applied to the active control piezoelectric layer, so as to replenish partial lost acoustic energy, improve the quality factor of the BAW sensor and then achieve the aim of improving the sensitivity of the BAW sensor. The sensor has the advantages that the sensor is simple in structure and can be manufactured by adopting the micromachining process flow of the conventional thin-film BAW resonator or sensor. The invention puts forward a solution for the sensitivity of thin-film BAW sensors, and the solution can also be applied to other acoustic wave sensors and acoustic wave resonators.

Description

Have the thin film acoustic wave sensor and the method that initiatively suppress the acoustical energy losses function

Technical field

The invention belongs to microelectromechanical systems (MEMS) field, specially refer to thin film bulk acoustic resonator (FBAR) and thin film acoustic wave sensor.

Background technology

Sensor is a basic means of obtaining information, and microelectromechanical systems (MEMS) technology has promoted sensor technology to the development of microminiaturized, integrated and intelligent direction, and the MEMS sensor also has low cost, low-power consumption, advantage such as easy of integration simultaneously.Sonic sensor is the general physics of a class, chemistry and biology sensor, have that easy and simple to handle, speed is fast, non-marked, highly sensitive, advantage such as sensing range is big, all have broad application prospects in fields such as Industrial Process Monitoring, environmental monitoring, clinical medical inspection, food security check, poison gas detection, drug developments.In recent years, as biology sensor, sonic sensor has been brought into play enormous function in the research of biopolymer, the biochemical film growth kinetics of self assembly, enzyme and DNA interaction, protein interaction, virus and bacterium, living cells adhesion behavior and aspects such as medicine and rake interaction, just progressively become a kind of important means of biochemical analysis.But, analytical approachs such as same mass spectrum, plasma resonance and elliptical polarized light are compared, the sensitivity of sonic sensor is relatively low, so sonic sensor is used also seldom in research fields such as the detection of low concentration micromolecule, drug screening and biomaterial screenings at present.In order further to enlarge the range of application of sonic sensor, must further reduce its cost, improve its sensitivity, the microminiaturization of sonic sensor and integrated be the effective means that reaches above target, become the current focus of research in the world.

Based on micro-processing technology, the thickness shearing mode film bulk acoustic biochemical sensor of succeeding in developing in the world, the vibration mode of this sensor is the same with conventional QCM (Quartz Crystal Microbalance), all is thickness shearing modes, therefore at liquid environment higher sensitivity is arranged also, be particularly suitable for biochemistry detection.For the energy leakage that reduces, thin film acoustic wave sensor generally adopts following two kinds of structures: (1) responsive piezoelectric membrane is fixed in substrate surface by Bragg reflecting layer; (2) responsive piezoelectric membrane below be metal electrode and support film, support film directly contacts with air.The energy leakage of the sound wave of second kind of structure is very little, the quality factor of sensor and highly sensitive, but the physical strength of this sensor construction is low, is damaged easily.First kind of sensor adopts Bragg reflecting layer that sound wave is limited in the sensitive layer as far as possible, because affixed with substrate, so sensor physical strength height, be difficult for being damaged; Bragg reflecting layer alternately is made up of high sound-resistance material of multilayer and low acoustic resistance material, and every layer thickness is quarter-wave, but because Prague emission layer still can cause the loss of acoustic wave energy, therefore the transducer sensitivity of this structure is lower relatively.

Summary of the invention

The objective of the invention is to propose a kind of active control technology that utilizes and improve thin film acoustic wave sensor sensitivity of method and structure.

For achieving the above object, the present invention takes following technical scheme:

Have the thin film acoustic wave sensor that initiatively suppresses the acoustical energy losses function and comprise that silicon chip, little processing are at on-chip insulation course, responsive piezoelectric layer, and the electrode that lays respectively at the upper and lower surface of responsive piezoelectric layer, little processing one ACTIVE CONTROL piezoelectric layer and relative bottom electrode between responsive piezoelectric layer bottom electrode and insulation course.When detecting, need detect the relevant control voltage of voltage with responsive piezoelectric layer by the ACTIVE CONTROL piezoelectric layer being applied one, it is effectively additional to realize that acoustic energy to loss carries out, and reaches the purpose of raising sensor quality factor and sensitivity.

Relation to ACTIVE CONTROL piezoelectric layer voltage that applies and the voltage that responsive piezoelectric layer is applied is determined by the following method:

(1) supposes to determine to be measured with thin film acoustic wave sensor i rank vibration frequency change.At first only the responsive piezoelectric layer of described thin film acoustic wave sensor being applied amplitude is V ₀Alternation detect voltage, record described thin film acoustic wave sensor and the corresponding quality factor q of i rank vibration frequency ₀, promptly the acoustic energy of each vibration loss is

$E_{c\max }=\frac{2\mathrm{\π}{E}_{p\max 0}}{Q_0}---\left(1\right)$

E wherein _Pmax0The expression sensor is detecting voltage V ₀Maximum flexibility potential energy when effect is vibrated down, E _CmaxThe expression sensor is at the acoustic energy of each vibration period internal cause loss;

(2) to detect voltage magnitude be V when being applied to alternation on the responsive piezoelectric layer _m, the alternation control voltage magnitude that is applied on the ACTIVE CONTROL piezoelectric layer is V _cThe time, according to the expectation quality factor q of sensor _eWith the acoustical energy losses characteristic that records by previous step, vibrated the acoustic energy that need obtain replenishing each time and be from the ACTIVE CONTROL piezoelectric layer

$E_s=\frac{2\mathrm{\π}{E}_{p\max }}{Q_0}-\frac{2\mathrm{\π}{E}_{p\max }}{Q_e}---\left(2\right)$

E wherein _PmaxBe the maximum flexibility potential energy of sensor in vibration processes.Quality factor q according to the vibration of i rank ₀And the vibration shape, obtain E _PmaxWith V _mAnd V _cRelation, promptly

E _pmax＝E _pmax(V _m，V _c，Q ₀) (3)

If detect voltage magnitude V _mConstant, the vibration shape according to the vibration of sensor i rank obtains V _cAdd to acoustic energy E in the sensor with each vibration period by the control piezoelectric layer _sRelation, promptly

E _s＝E _s(V _m，V _c，Q ₀) (4)

(3) bring formula (3) and formula (4) into formula (2), obtain and particular detection voltage V _mWith the expectation quality factor q _eCorresponding control voltage V _c

The present invention has following characteristics:

1, the method and structure that proposes of the present invention can carry out effectively additionally to the acoustic energy of sensor loss, realizes the raising of transducer sensitivity.

2, above film bulk acoustic biochemical sensor can utilize the micro fabrication flow process of existing thin film bulk acoustic resonator or sensor to make, and is simple in structure, is easy to realize.

3, the physical strength height of sensor is difficult for being damaged.

Description of drawings

The present invention is further described below in conjunction with drawings and Examples.

Fig. 1 is at silicon chip front growthing silica layer synoptic diagram

Fig. 2 is preparation and graphical ACTIVE CONTROL piezoelectric layer bottom electrode synoptic diagram

Fig. 3 is preparation and graphical ACTIVE CONTROL piezoelectric layer synoptic diagram

Fig. 4 is preparation and graphical responsive piezoelectric layer bottom electrode (being ACTIVE CONTROL piezoelectric layer top electrodes simultaneously) synoptic diagram

Fig. 5 is preparation and graphical responsive piezoelectric layer synoptic diagram

Fig. 6 is preparation preparation and graphical responsive piezoelectric layer top electrode synoptic diagram

Fig. 7 is the sensor sectional view

Embodiment

The present invention proposes has the thin film acoustic wave sensor that initiatively suppresses the acoustical energy losses function and can adopt silica-based micro-processing technology making, is a typical technological process below:

1, thermal oxide deposit S on the silicon chip 1 of twin polishing _iO ₂Layer 2 (being insulation course), thickness 100～500nm (as shown in Figure 1);

2, positive photoetching is 1 time, forms the photoresist figure, evaporation Pt electrode layer on substrate, and wet method is removed photoresist, forms ACTIVE CONTROL piezoelectric layer bottom electrode 3 figures (as shown in Figure 2) with the complementation of photoresist figure;

3, adopt sputtering method to prepare ZnO ACTIVE CONTROL piezoelectric layer, photoetching 2 times, etching ZnO piezoelectric layer is removed photoresist, forms ACTIVE CONTROL piezoelectric layer 4 figures (as shown in Figure 3);

4, positive photoetching is 3 times, forms the photoresist figure, evaporation Pt electrode layer, and wet method is removed photoresist, forms responsive piezoelectric layer bottom electrode 5 (this electrode the is ACTIVE CONTROL piezoelectric layer top electrodes simultaneously) figure (as shown in Figure 4) with the complementation of photoresist figure;

5, adopt sputtering method to prepare the responsive piezoelectric layer of ZnO, photoetching 4 times, etching ZnO piezoelectric layer is removed photoresist, forms responsive piezoelectric layer 6 figures (as shown in Figure 5);

6, positive photoetching is 5 times, forms the photoresist figure, evaporation Pt electrode layer, and wet method is removed photoresist, forms responsive piezoelectric layer top electrode 6 figures (as shown in Figure 6) with the complementation of photoresist figure.

The sectional view with the thin film acoustic wave sensor that initiatively suppresses the acoustical energy losses feature capability that obtains as shown in Figure 7.

When detecting, need apply one by the ACTIVE CONTROL piezoelectric layer to sensor and detect the relevant control voltage of voltage with responsive piezoelectric layer, definite method of this control voltage is seen the relevant portion in the summary of the invention.This control voltage will make the control piezoelectric layer that the acoustic energy of sensor loss is replenished, thereby improve the quality factor of sensor, the sensitivity that further improves sensor.

Claims (2)

1. has the thin film acoustic wave sensor that initiatively suppresses the acoustical energy losses function, it comprises that silicon chip, little processing are at on-chip insulation course, responsive piezoelectric layer, and the electrode that lays respectively at the upper and lower surface of responsive piezoelectric layer, it is characterized in that, little processing one ACTIVE CONTROL piezoelectric layer and relative bottom electrode between described responsive piezoelectric layer bottom electrode and insulation course, described bottom electrode is between ACTIVE CONTROL piezoelectric layer and insulation course; When detecting, detect the relevant control voltage of voltage by the ACTIVE CONTROL piezoelectric layer being applied one with responsive piezoelectric layer, realize the acoustic energy of loss is compensated, reach the purpose of raising transducer sensitivity;

Described relation to ACTIVE CONTROL piezoelectric layer control voltage that applies and the detection voltage that responsive piezoelectric layer is applied is determined by the following method:

(1) suppose to determine with thin film acoustic wave sensor i rank vibration frequency change to be measured, at first only the responsive piezoelectric layer of described thin film acoustic wave sensor being applied amplitude is V ₀Alternation detect voltage, record described thin film acoustic wave sensor and the corresponding quality factor q of i rank vibration frequency ₀, promptly the acoustic energy of each vibration loss is

$E_{c\max }=\frac{2{\mathrm{\πE}}_{p\max 0}}{Q_0}---\left(1\right)$

E wherein _Pmax0The expression sensor is detecting voltage V ₀Maximum flexibility potential energy when effect is vibrated down, E _CmaxThe expression sensor is at the acoustic energy of each vibration period internal loss;

(2) to detect voltage magnitude be V when being applied to alternation on the responsive piezoelectric layer _m, the alternation control voltage magnitude that is applied on the ACTIVE CONTROL piezoelectric layer is V _cThe time, according to the expectation quality factor q of sensor _eWith the acoustical energy losses characteristic that records by previous step, vibrated the acoustic energy that need obtain replenishing each time and be from the ACTIVE CONTROL piezoelectric layer

$E_s=\frac{{2\mathrm{\πE}}_{p\max }}{Q_0}-\frac{{2\mathrm{\πE}}_{p\max }}{Q_e}---\left(2\right)$

E wherein _PmaxBe the maximum flexibility potential energy of sensor in vibration processes, according to the quality factor q of i rank vibration ₀And the vibration shape, obtain E _PmaxWith V _mAnd V _cRelation, promptly

E _pmax＝E _pmax(V _m，V _c，Q ₀) (3)

If detect voltage magnitude V _mConstant, the vibration shape according to the vibration of sensor i rank obtains V _cAdd to acoustic energy E in the sensor with each vibration period by the control piezoelectric layer _sRelation, promptly

E _s＝E _s(V _m，V _c，Q ₀) (4)

(3) bring formula (3) and formula (4) into formula (2), obtain and particular detection voltage V _mWith the expectation quality factor q _eCorresponding control voltage V _c

2. utilize active control technology to improve the thin film acoustic wave sensor sensitivity of method, it is characterized in that: described method is on the thin film acoustic wave sensor that only has responsive piezoelectric layer, increase the ACTIVE CONTROL piezoelectric layer, and ACTIVE CONTROL port of corresponding increase, when detecting, when responsive piezoelectric layer is applied detection voltage the ACTIVE CONTROL piezoelectric layer is applied control voltage, effectively additional so that the acoustic energy that loses is carried out, reach the purpose that improves transducer sensitivity;

Described relation to ACTIVE CONTROL piezoelectric layer control voltage that applies and the detection voltage that responsive piezoelectric layer is applied is determined by the following method:

(1) suppose to determine with thin film acoustic wave sensor i rank vibration frequency change to be measured, at first only the responsive piezoelectric layer of described thin film acoustic wave sensor being applied amplitude is V ₀Alternation detect voltage, record described thin film acoustic wave sensor and the corresponding quality factor q of i rank vibration frequency ₀, promptly the acoustic energy of each vibration loss is

$E_{c\max }=\frac{{2\mathrm{\πE}}_{p\max 0}}{Q_0}---\left(1\right)$

E wherein _Pmax0The expression sensor is detecting voltage V ₀Maximum flexibility potential energy when effect is vibrated down, E _CmaxThe expression sensor is at the acoustic energy of each vibration period internal loss;

(2) to detect voltage magnitude be V when being applied to alternation on the responsive piezoelectric layer _m, the alternation control voltage magnitude that is applied on the ACTIVE CONTROL piezoelectric layer is V _cThe time, according to the expectation quality factor q of sensor _eWith the acoustical energy losses characteristic that records by previous step, vibrated the acoustic energy that need obtain replenishing each time and be from the ACTIVE CONTROL piezoelectric layer

$E_s=\frac{{2\mathrm{\πE}}_{p\max }}{Q_0}-\frac{{2\mathrm{\πE}}_{p\max }}{Q_e}---\left(2\right)$

E wherein _PmaxBe the maximum flexibility potential energy of sensor in vibration processes, according to the quality factor q of i rank vibration ₀And the vibration shape, obtain E _PmaxWith V _mAnd V _cRelation, promptly

E _pmax＝E _pmax(V _m，V _c，Q ₀) (3)

If detect voltage magnitude V _mConstant, the vibration shape according to the vibration of sensor i rank obtains V _cAdd to acoustic energy E in the sensor with each vibration period by the control piezoelectric layer _sRelation, promptly

E _s＝E _s(V _m，V _c，Q ₀) (4)

(3) bring formula (3) and formula (4) into formula (2), obtain and particular detection voltage V _mWith the expectation quality factor q _eCorresponding control voltage V _c

Images