LiNbO
3/ SiO
2/ diamond multilayer piezoelectric film and preparation method thereof
One, technical field
The present invention relates to piezoelectric film material, particularly a kind of LiNbO
3/ SiO
2/ diamond multilayer piezoelectric film and preparation method thereof.
Two, background technology
Along with the fast development of mobile communication technology, the frequency of utilization of surface acoustic wave (SAW) device improves constantly, and has developed into present GHz level from original M Hz level.As everyone knows, the raising of SAW device operating frequency is mainly passed through to shorten the interdigital electrode cycle or use high-sound-velocity material, yet for traditional surface acoustic wave material such as LiNbO
3, LiTaO
3Because surperficial velocity of wave is lower, the operating frequency that is issued to GHz in current process conditions is quite difficult, thereby the exploitation high-sound-velocity material becomes the technical bottleneck that improves SAW device operating frequency Deng materials such as monocrystal material or PZT series piezoelectric ceramic.
Diamond is as the fastest material of acoustic surface wave propagation in all substances, and acoustic wave propagation velocity is higher than more than the 10000m/s, is the ideal material of preparation high frequency SAW device.Yet because diamond itself does not have piezoelectricity, can't excite and receive surface acoustic wave, therefore need combine and form multi-layer film structure with piezoelectric membrane.LiNbO
3Because of its excellent piezoelectricity, electric light, acousto-optic and nonlinear optical properties, and be widely used in making in all kinds of fiber waveguides, optical switch and the SAW device.Compare LiNbO with ZnO with piezoelectrics such as AlN
3Have bigger electromechanical coupling factor, Theoretical Calculation shows c axle orientation LiNbO
3The acoustic surface wave propagation speed of/diamond multilayer structure is up to 12000m/s, electromechanical coupling factor can reach 9%[H.Nakahata, A.Hachigo, K.Higaki et al., IEEE Trans.Ultrason.Ferroelectr.Freq.Contr.42 (1995) 362.], so c axle orientation LiNbO
3/ diamond multilayer structural material has great application value and application prospect aspect broadband, the high frequency SAW device.
Yet because lattice mismatch is big between diamond and the lithium niobate, and diamond high temperature in oxygen atmosphere is easy to oxidation, thus on diamond the high c axle orientation of preparation LiNbO
3Film is difficulty very.In addition, LiNbO
3Because of having bigger temperature coefficient, will influence LiNbO
3Temperature stability and the quality and the result of use of/diamond multilayer membrane structure SAW device.H.K.Lam etc. are at diamond and LiNbO
3Introduce amorphous Al between the film
2O
3As resilient coating, adopt pulsed laser deposition technique to prepare the LiNbO of c axle orientation
3Piezoelectric membrane, but lithium phase [H.K.Lam, J.Y.Dai, H.L.W.Chan, Jpn.J.Appl.Phys.43 (2004) L706.] has appearred in the piezoelectric membrane significantly lacking.Application number be 200510014977.X patent disclosure a kind of LiNbO
3/ ZnO/ diamond multi-layered film structure surface acoustic wave device and preparation method thereof adopts radiofrequency magnetron sputtering technology growth c axle orientation LiNbO
3Piezoelectric membrane.Because LiNbO
3, ZnO, Al
2O
3With adamantine frequency-temperature coefficient TCF all less than zero (temperature coefficient of delay TCD is all greater than zero), thereby with ZnO, Al
2O
3For the temperature stability of the multi-layer film structure SAW device of resilient coating does not improve.
Three, summary of the invention
At above-mentioned situation, for overcoming the prior art defective, the present invention's purpose just provides a kind of LiNbO
3/ SiO
2/ diamond multilayer piezoelectric film and preparation method thereof, the temperature stability and the high c axle that can effectively solve the SAW device are orientated LiNbO
3Film preparation problem, the technical scheme of its solution are, at diamond substrate and LiNbO
3Introduce amorphous SiO between the piezoelectric membrane
2Resilient coating, its preparation method be, at first makes target with silicon (Si) on 200-400 ℃ diamond substrate, with pulsed laser deposition with amorphous SiO
2Be deposited on the diamond substrate, constitute amorphous SiO
2Resilient coating, amorphous SiO
2Buffer layer thickness is 0.05-0.6 μ m; Again with the amorphous SiO for preparing
2/ diamond substrate is warming up to 600-750 ℃, with LiNbO
3Be target, with pulse laser with LiNbO
3Be deposited on amorphous SiO
2On the resilient coating, LiNbO
3Deposit thickness is 0.2-3 μ m, constitutes LiNbO
3Amorphous SiO is arranged between piezoelectric thin film layer and the diamond substrate
2The composite piezoelectric film of resilient coating, SiO
2And LiNbO
3In pulsed laser deposition process, all need feed 99.99% high purity oxygen gas respectively, oxygen is pressed and is 15-70Pa, and laser single-pulse energy density is 3.0-4.5J/cm
2, the distance between target and the substrate is 3.5-6.0cm; LiNbO
3After the piezoelectric thin film layer deposition, in 99.99% high purity oxygen gas of 30-70Pa, be cooled to room temperature 18-25 ℃, the LiNbO of preparation
3Film is high c axle oriented film, and the present invention is simple in structure, method advanced person, science, and easily preparation when improving SAW device operating frequency, efficiently solves the temperature stability problem of SAW device, is the innovation on the piezoelectric membrane.
Four, description of drawings
Accompanying drawing is a structural representation of the present invention.
Five, embodiment
Below in conjunction with drawings and Examples the specific embodiment of the present invention is elaborated.
Provided by accompanying drawing, product of the present invention is at diamond substrate 1 and LiNbO
3Introduce amorphous SiO between the piezoelectric membrane 3
2 Resilient coating 2 constitutes, and its concrete preparation method is provided by following examples:
Embodiment one
1, diamond substrate (with preceding capable of washing clean) is put into pulsed laser deposition equipment vacuum chamber, be evacuated to 10
-3Pa, heated substrate to 300 ℃, (Si) makes target with silicon, and distance be 4.5cm between target and the diamond substrate, feeds 99.99% high purity oxygen gas, and oxygen is pressed and is 15Pa, usefulness pulse laser deposited amorphous SiO on diamond substrate
2Resilient coating, amorphous SiO
2Buffer layer thickness is 0.13 μ m;
2, will deposit amorphous SiO
2The diamond substrate of resilient coating is warming up to 680 ℃, feeds 99.99% high purity oxygen gas in deposition process, and oxygen is pressed and remained on 60Pa, and laser frequency is at 3Hz, with LiNbO
3Be target, distance is 3.5J/cm at 4cm with the single pulse energy metric density between target and the diamond substrate
2Laser at amorphous SiO
2Deposit thickness is the LiNbO of 0.45 μ m on the resilient coating
3Piezoelectric thin film layer;
3, LiNbO
3After piezoelectric thin film layer deposition finishes, depress in 99.99% high purity oxygen of 60Pa and to be cooled to 20 ℃, obtain the LiNbO of surfacing
3/ SiO
2/ diamond multilayer piezoelectric film, the LiNbO of preparation
3Film is high c axle oriented film, and its crystal grain dimension is 95nm, and surface average roughness is 14.3nm.
Embodiment two
1, diamond substrate (with preceding capable of washing clean) is put into pulsed laser deposition equipment vacuum chamber, be evacuated to 10
-3Pa, heating diamond substrate to 350 ℃ is made target with silicon, carries out SiO in the 99.99% high purity oxygen gas atmosphere of 15Pa
2Deposition, between target and the substrate distance at 5.7cm, be the amorphous SiO of 0.3 μ m with pulse laser deposit thickness on diamond substrate
2Resilient coating;
2, will deposit amorphous SiO
2The diamond substrate of resilient coating is warming up to 640 ℃, feeds 99.99% high purity oxygen gas in deposition process, and oxygen is pressed and remained on 40Pa, and laser frequency is at 3Hz, with LiNbO
3Make target, distance is 4J/cm at 4.5cm with the single pulse energy metric density between target and the diamond substrate
2Laser at amorphous SiO
2Deposit thickness is the LiNbO of 0.6 μ m on the resilient coating
3Piezoelectric thin film layer;
3, LiNbO
3After piezoelectric thin film layer deposition finishes, depress in 99.99% high purity oxygen of 40Pa and to be cooled to 25 ℃, obtain the LiNbO of surfacing
3/ SiO
2/ diamond multilayer piezoelectric film, the LiNbO of preparation
3Film is high c axle oriented film, and its crystal grain dimension is 105nm, and surface average roughness is 16.5nm.
To the above-mentioned product LiNbO for preparing3/SiO
2/ diamond multilayer piezoelectric film experiment showed, amorphous SiO after deliberation2Temperature coefficient to sandwich construction has compensating action, one of best means of at present multi-component oxide film growth of pulsed laser deposition technique conduct, compare with sputtering technology to have and can keep the advantages such as target and film composition be consistent, pulsed laser deposition technique is conducive to the c-axis oriented growth of film simultaneously. The present invention is at diamond and LiNbO3Introduce and LiNbO between the film3Amorphous SiO with opposite temperature coefficients2As cushion, adopt pulsed laser deposition to prepare c-axis orientation LiNbO3Piezoelectric membrane so both can suppress the high-temperature oxydation on diamond film surface in the oxygen atmosphere and improve diamond and LiNbO3Between bigger lattice mismatch issue, can improve by compensating action again simultaneously the temperature stability of multi-layer film structure. Therefore, the present invention compares with technology with current material, and the present invention has following outstanding advantage:
(1) employing and diamond and LiNbO3Amorphous SiO with opposite temperature coefficients2As cushion, but establishment diamond and LiNbO3Between bigger lattice mismatch and the problem of diamond surface high-temperature oxydation, obtain the c-axis orientation LiNbO of surfacing3Film, the while can be improved by compensating action again the temperature stability of multilayer piezoelectric film, and the temperature coefficient of this multilayer piezoelectric film can pass through amorphous SiO2Thickness compensate adjusting;
(2) this multilayer piezoelectric film can satisfy the application demand in high electromechanical coupling factor, high frequency, fields such as high-performance SAW (Surface Acoustic Wave) device that temperature stability is good.