CN101526394B

CN101526394B - Low-frequency vibration measuring device

Info

Publication number: CN101526394B
Application number: CN2009101063736A
Authority: CN
Inventors: 彭本贤; 俞挺; 于峰崎
Original assignee: Shenzhen Institute of Advanced Technology of CAS
Current assignee: Zhuhai Institute Of Advanced Technology Chinese Academy Of Sciences Co ltd
Priority date: 2009-03-31
Filing date: 2009-03-31
Publication date: 2012-02-15
Anticipated expiration: 2029-03-31
Also published as: CN101526394A

Abstract

The invention relates to a low-frequency vibration measuring device, comprising a vibration sensor and a CMOS chip, the vibration sensor is integrated on the CMOS chip, the vibration sensor is a micro electro mechanical system (MEMS) containing a sensing element; wherein, the sensing element comprises an FET containing an air gate dielectric and a floating gate, an vibration-inducing mass block containing a metal gate is installed opposite to the floating gate, the vibration of the mass block causes change of the coupling capacitance between the floating gate and the metal gate, and causes drain current change of the FET. Vibration information can be obtained by measuring current, in addition, the coupling capacitance between the floating gate and drain is used to increase transconductance, thus improving sensitivity and realizing the purpose of measuring low-frequency vibration.

Description

Low-frequency vibration measuring device

[technical field]

The present invention relates to a kind of vibration measurement device, especially relate to a kind of low-frequency vibration measuring device.

[background technology]

In some field, very low as the frequency of vibrations such as large rotating machine device, heavy construction structure, skyscraper, bridge dam, generally require surveying instrument can measure the low-frequency vibration about 0.5Hz.For low frequency and even ultra-low frequency signal (≤0.1Hz) be the difficult point of many domestic and international measurement and analysis instruments, for≤0.01Hz even to the extremely low frequency signal of 0.001Hz, their Measurement and analysis almost is a blank.Low-frequency vibration is monitored and fault diagnosis, all need high sensitivity and high reliability to satisfy the needs of security.The vibration of genset like monitoring is given security for the genset safe operation.Bridge self-vibration characteristic test is for confirming that the bridge running status provides foundation, when bridge load operation all the year round, or suffers accidental impact, and the duty of bridge might change.The bridge self-vibration characteristic also possibly cause influencing vehicle and bridge resonates.Along with the development of exploration engineering, the demand that is used to accept the wave detector of seismic signal grows with each passing day, and has proposed higher technical requirement.At present; The frequency effective range of the vibration transducer that in seismic prospecting, generally uses is between 5Hz～500Hz; Seismic signal below the 5Hz is difficult to accurately measure, and these low-frequency information are very useful to the inverting stratal configuration, but seismoreceiver never has big breakthrough.Because such sensor can not get desirable original signal, has become one of main bottleneck of petroleum exploration.The maximum drawback of this type wave detector is exactly that sensitivity is low at present.The 2nd, the signal to noise ratio (S/N ratio) that low-frequency range is low.Because the vibration frequency about 1Hz has proposed harsh requirement to the low frequency characteristic of inertia-type sensor; Yet such sensor is because the inherent shortcoming of its physical construction at present; At ultralow frequency range (1Hz and following); Its output signal " flooding " fully is difficult to realize the accurate measurement to vibration parameters in noise.Therefore the detection of ultralow frequency absolute vibration is a great problem in engineering test field always.

[summary of the invention]

In view of this, be necessary to provide a kind of highly sensitive low-frequency vibration measuring device that has.

A kind of low-frequency vibration measuring device; Involving vibrations sensor and CMOS chip, said vibration transducer are integrated on the said CMOS chip, and said vibration transducer comprises sensing unit; Said sensing unit comprises the FET that contains floating boom and has embedded metal or polycrystalline silicon material and be used for the mass of induction vibration as grid; Said floating boom embeds in the dielectric layer of CMOS chip, and said mass places the opening of CMOS chip medium layer, and corresponding setting with FET; Be the silica medium layer of air dielectric layer and CMOS chip between said mass and the FET, make grid and floating boom be oppositely arranged.

The overlap capacitance of utilizing floating boom and drain electrode to constitute, and the mutual conductance that increases FET; Grid changes the coupling capacitance of grid and floating boom formation with the vibration of mass, and then changes the output current size of FET, thereby can measure low-frequency vibration, reaches highly sensitive effect.

In a preferred embodiment, be provided with cantilever in the said dielectric layer, said mass places on the said cantilever, makes the mass can free vibration.

In a preferred embodiment, said FET is thick oxygen transistor, can improve the ratio of the coupling capacitance of floating boom and drain electrode in total capacitance, thereby further improves sensitivity.

In a preferred embodiment, said FET is the nature FET, and said natural FET directly is built on the substrate, and its channel doping concentration is 3 * 10 ¹⁵/ cm ³-1 * 10 ¹⁶/ cm ³Low doping content has reduced impurity scattering, has improved signal to noise ratio (S/N ratio).Because grid is unsettled; The low-frequency noise that causes thereby the ditch that the gate oxidation layer charge fluctuation that reduces unit area causes is led the fluctuation of mobility; And reduced the noise that gate leakage current and sub-threshold leakage current cause, thereby improved output current and keep low noise.

[description of drawings]

Fig. 1 is the structural representation of low-frequency vibration measuring device;

Fig. 2 is the structural representation of measurement mechanism groundwork part;

Fig. 3 is the equivalent circuit diagram of structure shown in Figure 2;

Fig. 4 is vibration displacement-output current figure;

Fig. 5 is the amplitude versus frequency characte figure of 0.05g inertial acceleration lower sensor;

Fig. 6 is the noise-frequency comparison diagram of nature FET and conventional FET.

Further explain below in conjunction with accompanying drawing.

[embodiment]

A kind of low-frequency vibration measuring device, involving vibrations sensor and CMOS chip, said vibration transducer are integrated on the same CMOS chip; Said vibration transducer is the microelectromechanical systems (MEMS) that comprises sensing unit; Wherein sensing unit is that grid is floated, and promptly has the FET of floating boom, utilizes the coupling capacitance of floating boom and drain electrode to increase mutual conductance; Thereby raising sensitivity reaches the purpose of measuring vibrations.

At first, in layout design, select 0.18 μ m mixed signal technology for use, the thick oxygen FET of 3.3V and natural FET (Native MOS) in SPICE technology library Modeling and Design.FET breadth length ratio W/L is 208, and FET grid length is 1.2 μ m, grid width 250 μ m.Utilize CMOS technology to realize then.Do not have mask dry etching and wet etching after the CMOS flow and discharge microstructure.

The CMOS chip forms structure as shown in Figure 1 through dry etching and wet corrosion technique.Outer layer metal film 1 covers on the silica medium layer 21 of CMOS chip, is integrated on the CMOS chip as the FET 3 of the sensing unit of microelectromechanical systems (MEMS).Wherein FET 3 comprises the thick oxygen gate oxide 34 between floating boom 31, source electrode (not indicating), drain electrode 32, substrate 33 and floating boom 31 and the substrate 33.Floating boom 31 places the silica medium layer 21 of said CMOS chip.

Opening 22 is arranged on the CMOS chip, and the silica medium layer 21 of the position corresponding with floating boom 31 is provided with the grid that comprises metal material in opening 22, i.e. the mass 5 of metal gates 4, and FET 3 is oppositely arranged with mass 5.Slot milling between mass 5 and FET 3 forms air dielectric layer 6.

In dielectric layer 21, also be provided with cantilever 7, mass 5 places on the cantilever 7, and mass 5 can free vibration on cantilever 7.

The synoptic diagram of the groundwork part of present embodiment medium and low frequency vibration measurement device is as shown in Figure 2, and the floating boom 31 of FET does not join with other interconnection line, its mass 5 that comprises metal gates 4 that is provided with spaced above, and mass 5 can up-down vibration.Its equivalent working circuit diagram is as shown in Figure 3, and the principle of work of measurement is following:

In conjunction with Fig. 2, on metal gates 4, add a clock pulse signal voltage of CMOS chip, mass 5 vibrations make metal gates 4 and floating boom 31 couplings form variable capacitance C _FgVariable capacitance C _FgCapacitor C with the thick oxygen gate oxide 34 of FET _OxPolyphone.Because the voltage that the clock pulse signal frequency far above the vibration frequency of vibration transducer mass 5, is added on the metal gates 4 is given variable capacitance C _FgWith capacitor C _OxCharging, and reach equilibrium state rapidly.In a certain moment of vibration, can think variable capacitance C _FgIt is fixed capacity.Because also there is coupling capacitance C in floating boom 31 with drain electrode 32 _Fd, when distinguishing making alive V at drain electrode 32 and metal gates 4 _DAnd V _GThe time, through drain 32 with the coupling capacitance C of floating boom 31 _FdAnd variable capacitance C _FgOn floating boom 31, induce noble potential.Mass 5 is at arbitrary moment in per 1/4 cycle of its vibration, variable capacitance C _FgIt is constant capacitance that charging just reaches after the balance having different, so different induced electric fields changes the electrical conductance of the following channel region of floating boom 31.And then drain current changes, and obtains vibration signal according to the drain current that measures.

In the present embodiment, the FET of selecting for use is thick oxygen transistor, since thick oxygen characteristics of transistor, the coupling capacitance C of floating boom and drain electrode _FdRatio regular meeting in total capacitance is bigger than the transistorized ratio of other types, increases C _FdRatio in total capacitance can make the change in voltage on the floating boom obvious, thereby the electric conductivity of raceway groove in the FET is changed, and improves the sensitivity of FET in measurement, improves the effect of measuring low-frequency vibration.

Utilize the HSPICE Simulation result as shown in Figure 4, when the movable clearance of the grid of mass and the coupling capacitance of floating boom is 0～100nm, the sensing unit that single FET constitutes, the drain electrode output current that measures is between 3.8mA～6.0mA.And in Fig. 5, under the inertial acceleration of vibration transducer inertial force, resolution is the 0.05g/1.5 dust, so susceptibility reaches 3.7 μ A/0.05g.。

In addition; FET is nature FET (Native MOS), and is as shown in Figure 2, and natural FET directly is built on the lightly doped P type substrate; Do not need extra mask plate with the complete compatibility of the commercial CMOS technology of standard, the doping content of its raceway groove is 3 * 10 ¹⁵/ cm ³-1 * 10 ¹⁶/ cm ³, the FET with this doping content, its threshold voltage approach zero volt, thereby improve output current and keep low noise and eliminated the noise that trap/the body mutual conductance causes.Utilize the HSPICE Simulation result as shown in Figure 6, as can be seen from the figure, natural FET has extremely low noise with respect to the metal-oxide-semiconductor of routine.

In Fig. 1, also can see; The space that grid 4 and floating boom are 31 is divided into two parts; Be that a part is an air layer 6; A part is the dielectric layer 21 of CMOS chip, and the benefit of this kind structure is can avoid because of electrostatic force produces the adhesive phenomenon above causing mass sharply to move down after the elastic restoring force, and causing can't return.

The above embodiment has only expressed one embodiment of the present invention, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to claim of the present invention.Should be pointed out that for the person of ordinary skill of the art under the prerequisite that does not break away from the present invention's design, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection domain of patent of the present invention should be as the criterion with accompanying claims.

Claims

1. low-frequency vibration measuring device, involving vibrations sensor and CMOS chip is characterized in that; Said vibration transducer is integrated on the said CMOS chip; Said vibration transducer comprises sensing unit, and said sensing unit comprises the FET that contains floating boom and embedded metal or polycrystalline silicon material and be used for the mass of induction vibration as grid that said floating boom embeds in the silica medium layer of CMOS chip; The mass vibration makes grid and floating boom coupling form variable capacitance; Form coupling capacitance between the drain electrode of floating boom and FET, when drain and gate difference making alive, said coupling capacitance and variable capacitance induce noble potential on floating boom; Said mass places the opening of CMOS chip silica medium layer; And corresponding setting with FET, between said mass and the FET silica medium layer of air dielectric layer and CMOS chip, make grid and floating boom be oppositely arranged.

2. low-frequency vibration measuring device as claimed in claim 1 is characterized in that, is provided with cantilever in the said silica medium layer, and said mass places on the said cantilever, makes the mass can free vibration.

3. low-frequency vibration measuring device as claimed in claim 1 is characterized in that, said FET is thick oxygen transistor.

4. low-frequency vibration measuring device as claimed in claim 1 is characterized in that, said FET is the nature FET, and said natural FET directly is built on the substrate, and its channel doping concentration is 3 * 10 ¹⁵/ cm ³-1 * 10 ¹⁶/ cm ³