CN1030590C

CN1030590C - Crystal pressure-sensitive element using pseado surface wave

Info

Publication number: CN1030590C
Application number: CN 92102637
Authority: CN
Inventors: 林江; 武树岭; 季朋义; 范加玲; 张滨华; 陈秀英; 王群; 潘洪泉
Original assignee: No49 Inst Ministry Of Machine-Building And Electronics Industry
Current assignee: No49 Inst Ministry Of Machine-Building And Electronics Industry
Priority date: 1992-03-27
Filing date: 1992-03-27
Publication date: 1995-12-27
Anticipated expiration: 2007-03-27
Also published as: CN1067963A

Abstract

The present invention discloses a crystal pressure-sensitive element using pseudo surface waves. The present invention utilizes favorable elasticity, piezoelectricity and temperature stability of a crystal material and also introduces a mode of pseudo surface waves with high operating frequencies into a sensor working mechanism, wherein the stability of the pseudo surface waves is higher than that of Rayleigh waves (generally named as surface acoustic waves) by nearly one order of magnitude. The present invention provides a harmonic operation 4-finger-3-finger interdigital electrode (a dividing-parallel connecting-suspension type interdigital structure) and a multifunctional energy collector to obtain the pressure-sensitive element having the advantages of high pure frequency spectrum, high loading capacity and adjustable temperature characteristic.

Description

Crystal pressure-sensitive element using pseado surface wave

Patent of the present invention relates to pressure sensitive device.Especially a kind of crystal pressure-sensitive element using pseado surface wave.

In the last few years, a kind of high performance novel sensor-crystal surface wave pressure sensor (SAWPS) had appearred both at home and abroad.The patent that relates to this kind sensor is more, and as United States Patent (USP) 3848144,3863493,3978731, a day disclosure is speciallyyed permit clear 61-207942, Soviet Union's invention 742734 and 1177696A etc.Present crystal surface wave pressure sensor all uses R wave pattern (Rayleigh wave) to be commonly called as surface acoustic wave.Strictly speaking, should be called quartzy R wave pressure transducer.Its cardiac component is quartzy R wave pressure-sensing device.

Fig. 1 is the exemplary block diagram of the present delay line type Rayleigh surface wave pressure-sensing device that uses.

The 1st, the piezoelectric quartz single-chip (being commonly called as quartzy substrate) through grinding and polishing adopts rectangle usually, and applies acoustic absorbant at its edge, and for example: sound absorbent rubber, epoxy resin etc. are to suppress the substrate edge acoustic reflection.A, B, C, D are interdigital transducer (IDT).Because of its shape is gained the name as the finger of fork.When adding electric signal on input IDT A, the C, then on crystal surface, encouraged R wave wave beam 8 and propagated into output IDT B and D.In order to improve pressure sensitivity, utilize Mechanical Method (grinding, ultrasonic machining etc.) or chemical etching method to make blind hole 2 at the back side of substrate and be commonly called as crystal cup.IDTA comprises the electrode section M of

ultrasonic bond electrode

4 and 5, bus-bar 6,7 and n repetition period ₁, M ₂M _nUsually get n=100～1000.In each repetition period electrode, M for example ₁(frame of broken lines) has 4 to refer to N in the section ₁, N ₂, N ₃, N ₄, N wherein ₁, N ₂Adjacent and link to each other N with last bus-bar 6 ₃, N ₄Adjacent and link to each other with bus-bar 7.N ₁, N ₂With N ₃, N ₄Pitch mutually.The gap of the finger beam of every interdigital electrode, Interdigital Space and adjacent bus-bar is λ s/8, the rayleigh wavelength of crystal when λ s is centre frequency in the formula.

When being added on the crystal cup by measuring pressure, crystal cup diaphragm 3 produces strains, and the characteristic that then makes its surface go up the R wave of propagating 8 changes, when with the external circuit formation oscillator that links, then its frequency changes thereupon.Therefore can record the size of pressure.A, the B structure of the C of IDT C, the structure of D and IDT are identical, and the purpose that IDT C, D are set is in order to utilize the difference frequency principle, to carry out temperature compensation.There is some problem in this kind sensitive element at present: the particle displacement amplitude of R wave is along with the degree of depth is exponential damping, and its energy overwhelming majority concentrates in the scope of the wavelength in surface.Therefore, the defective of crystal surface (dislocation etc.), surface working defective, cut, dust etc. all can influence the propagation characteristic of R wave.In addition, any solid, liquid contact with the physics of crystal cup upper surface and all can make the R wave amplitude that very high attenuation takes place, and make the blocking of oscillator.Therefore, the R wave pressure-active element can not carry out surface passivation or at pilot liquid such as its enclosure filling silicone oil, chip and test environment be isolated.This has seriously limited it and has used under rugged surroundings.

The objective of the invention is to: at the problems referred to above, provide a kind of pressure resolution big, temperature stability is good, and long-time stability are good, and can carry out the crystal pressure-sensitive element using pseado surface wave of surface passivation and (perhaps) filling pilot liquid.

The technology of the present invention solution:

The interdigital transducer (IDT) of input, output terminal be respectively four refer to, three refer to-cut apart, in parallel, floated.Concrete structure is:

Each period range Q of input end interdigital transducer E, G _n, T _n(n=100～1000) are provided with eight finger electrode V with bus-bar symmetry in the input end ₁～V ₄And u ₁～u ₄; Refer to electrode V ₃, V ₄And u ₃, u ₄Symmetry is connected in bus-bar in the input end; Refer to electrode V ₁, u ₁Be connected to the upper and lower bus-bar of input end with bus-bar symmetry in the input end; And, referring to electrode V ₁And V ₃Between, u ₁And u ₃Between a suspension be set respectively refer to electrode V ₂And u ₂And at each period range J of output terminal interdigital transducer F, H _n, P _n(n=100～1000) are provided with six finger electrode W with bus-bar symmetry in the output terminal ₁～W ₃And R ₁～R ₃; Refer to electrode W ₁, R ₁Symmetry is connected in bus-bar in the output terminal; Refer to electrode W ₂, R ₂Be connected to the upper and lower bus-bar of output terminal with bus-bar symmetry in the output terminal; Refer to electrode W ₃, R ₃Be suspended in respectively and refer to electrode W ₂, R ₂A left side then.

Advantage of the present invention:

1, it has reduced pseudo surface wave electrode V widely ₁, V ₂V _n, u ₁, u ₂U _n, W ₁, W ₂W _n, R ₁, R ₂R _nOn reflection.Other subharmonic or first-harmonic are setovered mutually because the harmonic wave that needs is overlapped these two kinds of IDT, so frequency spectrum is clean, thereby can obtain identical with the insertion loss of conventional design and sensitive element harmonic wave and clutter inhibition raising 15～20dB.

2, the wide conventional IDT than first-harmonic work of the bar of the metal finger electrode of this structure refers to that electrode is wide more than 2～3 times, has therefore improved yield rate greatly.

3, the motional impedance of this kind IDT be higher than conventional IDT and static capacity less than conventional IDT, so its impedance is higher, is convenient to realize gripping altogether coupling or image impedance coupling with amplifier, has improved its load capacity and has improved design freedom simultaneously.

Below in conjunction with accompanying drawing 2 most preferred embodiment of the present invention is described:

In the accompanying

drawing

2,1 piezoelectric quartz single-chip, E, F, G, H interdigital transducer (IDT), 2 crystal cups, 3 glasss of bottom diaphragms, 4,5,9,15,16,17 ultrasonic bond electrodes, bus-bar, Q under bus-bar, 14 output terminals in bus-bar, 13 output terminals on bus-bar, 11 multifunctional energy drip catchers, 12 output terminals in bus-bar, 8 pseudo surface wave wave beams, 10 input ends under bus-bar, 7 input ends on 6 input ends ₁～Q _n, T ₁～T _n(n=100～1000) input end cycle electrode section, V ₁～V ₄, u ₁～u ₄Corresponding Q ₁The finger electrode of section, J ₁～J _n, P ₁～P _n(n=100～1000) output terminal cycle electrode section, W ₁～W ₄, R ₁～R ₄Corresponding J ₁The finger electrode of section.In the present embodiment: each refers to that the width of electrode refers to gaps between electrodes and refers to that the gap of electrode and adjacent bus-bar is 3 λ input IDT ₀/ 8; Each refers to that the width of electrode refers to gaps between electrodes and refers to that the gap of electrode and adjacent remittance bar is λ output IDT ₀/ 3 and in input, the end of bus-

bar

10,13 is provided with a

ultrasonic bond electrode

17 and 16 respectively in the output terminal.In addition, the multifunctional energy drip catcher 11 among this figure, its structure can be 1～20(n=1～20 of input end or output terminal interdigital transducer (IDT)) (promptly the structure of this drip catcher is Q to individual period range _nOr J _n＜n=1～20 〉) or be the aluminium film.Drip catcher 11 among Fig. 2 is Q _nStructure, wherein 18,19 be the ultrasonic bond electrode of this device, the purpose that this drip catcher is set is because propagate on the pseudo surface wave limit, and the limit is to the auxilliary energy of penetrating of crystals, so as E, the G of IDT, with IDT F, H distance far the time, loss is too big.After adding the energy capture device, changed pseudo surface wave and propagated boundary condition, made it reduce energy along the propagation of quartzy top layer and sew, its effect is as follows:

(1) reduce the insertion loss, (2) suppress input as guarded electrode, and the electromagnetism between the output IDT directly is coupled, and (3) load as the quality of pseudo surface wave lag line, and fine-tuning frequency also can be adjusted temperature characterisitic.

Below in conjunction with Fig. 2 its course of work is described:

Put device (not drawing among the figure) when IDT E, G and IDT F, H and wideband low noise radio frequency and connect, constitute the pseudo surface wave oscillator, the cut type of crystal cup is that Y revolves-60 °～-45 °, Z ' propagation or Y revolves 30 °～55 °, Z ' propagation.When pressure was added on the crystal cup diaphragm 3, because the effect of pressure, the density of diaphragm material, elastic constant, piezoelectric constant and propagation distance changed, thereby cause the variation of oscillator frequency.Therefore, according to the change of frequency, can gaging pressure.

Claims

1, a kind of crystal pressure-sensitive element using pseado surface wave, form by single crystal quartz sheet and evaporation aluminium film, golden film or other metal film thereon, and on this kind metal film, form interdigital transducer by photoetching method, this interdigital transducer comprises several period ranges, each period range is four finger structures, equidirectional N ₁, N ₂Refer to and backward N ₃, N ₄Fourchette connects, and makes a blind hole that is called crystal cup at the single crystal quartz sheet back side that is loaded with input interdigital transducer and output interdigital transducer, the invention is characterized in:

Each period range Q of a, input end interdigital transducer E, G _n, T _n, eight finger electrode V with 10 symmetries of bus-bar in the input end are set ₁～V ₄And u ₁～u ₄, footnote n is between 100 to 1000;

Refer to electrode V ₃, V ₄And u ₃, u ₄Symmetry is connected in bus-bar 10 in the input end; Refer to electrode V ₁, u ₁With 10 symmetries of bus-bar in the input end, be connected to the upper and lower bus-bar 6,7 of input end; And, referring to electrode V ₁And V ₂Between, u ₁, u ₃Between a suspension be set respectively refer to electrode V ₂And u ₂

Each period range Jn, Pn of b, output terminal interdigital transducer F, H are provided with six finger electrode W with 13 symmetries of bus-bar in the output terminal ₁～W ₂And R ₁～R ₃, footnote n is between 100 to 1000;

Refer to electrode W ₁, R ₁Symmetry is connected in bus-bar 13 in the output terminal; Refer to electrode W ₂, R ₂Be connected to the upper and lower bus-bar 12,14 of output terminal with 13 symmetries of bus-bar in the output terminal; Refer to electrode W, R ₂Be suspended in respectively and refer to electrode W ₂, R ₂The left side.

2, crystal pressure-sensitive element using pseado surface wave according to claim 1, its feature:

In input, between the output terminal interdigital transducer, insert a multifunctional energy drip catcher 11, its structure is: it can be 1～20 period range of input end E, G or output terminal F, H interdigital transducer, or is the aluminium film.

3, crystal pressure-sensitive element using pseado surface wave according to claim 1, its feature:

Each refers to the width of electrode a, input interdigital transducer, refers to gaps between electrodes and refers to electrode and the gap of adjacent bus-bar is 3 λ ₀/ 8;

Each of b, output interdigital transducer refers to that the width of electrode refers to gaps between electrodes and refers to electrode and the gap of adjacent bus-bar is λ ₀/ 3;

An end of bus-bar 10,13 in c, input, the output terminal is provided with a ultrasonic bond electrode 9 and 15 respectively.