摘要
由于声表面波器件具有小型化、多功能、高频率、高可靠性和数字输出等特性,目前已被广泛应用于移动通信、航空航天、雷达、电子对抗、遥控遥测、广播电视等各类军用和民用电子系统中。因其应用潜力巨大,发展前景广阔,故对声表面波器件的研究具有重大的意义。
本文主要是对声表面波器件的制备工艺进行探索,同时,对由声表面波器件构成的振荡电路进行研究。对于声表面波器件的制备主要是高质量压电基底的制备和作为激励、检测信号用的叉指换能器的设计与制做。对于振荡电路的研究主要集中于电路的设计与仿真。
选用PZT压电薄膜作为声表面波器件的压电材料层,基片采用的是Au/Cr/SiO2/Si的多层膜结构。通过添加黏结剂聚乙烯吡咯烷酮(PVP),成功的制备出致密、无裂痕的PZT压电薄膜,经XRD测试,证明了该薄膜具有较好的取向性。在PZT压电薄膜的制备过程中,对富铅度和黏结剂的浓度等关键问题进行了研究。实验证明,在不添加黏结剂的情况下,当退火温度为700℃时,PZT薄膜中铅的含量几乎没有损失。为了既保证PZT薄膜不开裂,又保证PZT薄膜具有一定的厚度,经过大量的反复实验,最终将黏结剂的浓度选定为0.001～0.0015mol/L。最后,对所制备的PZT薄膜的电性能进行了研究,如电滞回线、压电系数和介电常数。其中,Pr=25μc/cm2,Ec=25KV/cm; d 33( eff )=210pC/N;εr=1130F/m。
叉指换能器的主要设计参数包括:叉指对数N、叉指周期节长度P、指宽d、指间距b、声孔径w和中心间距L等。本文对各参数设计进行了理论分析,并结合实验室现有的工艺条件,设计出指宽为10μm的叉指换能器的版图。先采用超微粒干版试做版,但由于超微粒干版的质量问题,最后采用47所提供的铬版。对实验室现行的光刻工艺进行了细节上的改良,最后成功的制备出声表面波器件。但叉指换能器经SEM测试发现,指宽约为12μm,指间距约为8μm。两者与设计值相比,略有偏差,在论文中对可能产生偏差的原因进行了分析。
对于声表面波振荡电路的研究,侧重于对振荡电路的设计与仿真,包括振荡电路起振条件和电路结构分析等问题。
Surface acoustic wave device has some characteristics, such as miniaturization、multifunction、high frequency、high reliability、digital output and so on. So surface acoustic wave device is widely used in many kinds of electronic systems of military and civil, such as mobile communications、aviation and spaceflight、radar、electronic counterwork、telecontrol and telemetry、television and so on. Surface acoustic wave device has great potential in application and wider foreground in development, so it is significative to investigate surface acoustic wave device.
The fabricate technology of surface acoustic wave device is mainly explored in this paper, at the same time oscillator consisted by surface acoustic wave device is investigated. It is mainly to fabricate high quality piezoelectric substrate and design interdigital transducers which are used to bestir and detect signals for surface acoustic wave device. It is mainly to focus investigation on design and simulation of circuit for oscillator.
PZT piezoelectric thin film was chosen as piezoelectric material layer of surface acoustic wave device, multilayer structure of Au/Cr/SiO2/Si was adopted as substrate. It was successful to fabricate PZT piezoelectric thin film which was dense and crackless by appending adhesive named polyvinylpyrrolidone, and the PZT film had better tropism by XRD testing. Some key problems were investigated during the fabrication processes of PZT piezoelectric thin film, such as excess of lead, concentration of adhesive and so on. When the anneal temperature was at 700℃, the experiment proved that without adhesive there was no loss of lead in PZT thin film. Concentration of adhesive was selected between 0.001 mol/L and 0.0015mol/L by repeat experiments in order to ensure that PZT thin film was crackless and had definite thickness. At last, electric characteristics of PZT thin film were investigated, such as P-E hysteresis loop-line、piezoelectric coefficient and dielectric constant: Pr=25μc/cm~2, Ec=25KV/cm; d 33 ( eff )=210pC/N;εr=1130F/m.
The mainly parameters of interdigital transducers (IDT) contain pairs of fingers of IDT(N)、length of period(P)、width of finger(d)、distance between neighbour fingers(b)、aperture(w)、distance between the centers of the IDT(L) and so on. Each parameter was analyzed in theory in this paper. According to existing technology condition in laboratory, the layout of IDT was designed, and the width of finger was 10μm. Ultrafine-grain plate was adopted to make edition in experiment, but quality of edition was disqualification, so chromium edition was offered by 47 research institute. Photolithography technology was improved in detail in laboratory, and surface acoustic wave device was successful made. When the IDTs were tested by SEM, it was found that the width of finger was nearly 12μm, and the distance between neighbour fingers was nearly 8μm. They were different from the design values, the reasons which may cause the differences were analyzed in this paper.
Design and simulation of oscillator were investigated in this paper, it contained some problems such as the surge condition of oscillator, analysis of circuit’s structure and so on.
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