Hypersonic Substrate Piezoelectric Thin Films And Surface Acoustic Wave Devices Developed To Explore

As the processing information amount of modern electronics increases rapidly,the carrier wave in communication must move to higher frequency band Thedeveloping 900M/l8GHz GMS (Global Mobile-communication System) is atypical example Surface acoustic wave (SAW) filter is one of the key elements inmodern wireless mobile-communication System The central operating frequencyof SAW filter (f) is defined as f=V/L, among which V means the SAW speed ofthe used material, and L is the period of its interdigital transducer(IDT) At present,it is difficult for SAW devices operating under GHz frequency because of thelimitation of materials and fabrication technology Diamond and silicon carbide(SiC) have a very high acoustic speed, and it is possible to fabricate GHz SAWdevices using piezoelectric films on diamond and SiC substrates based on thepresent technology Nowadays, it is competition to fabricate GHz SAW devicesusing diamond and SiC substrates In this thesis, we deposited zinc oxide (ZnO)films on diamond and SiC substrates and aluminum nitride (AlN) films on Sisubstrates with ZnO buffer by pulsed laser deposition (PLD) We have alsoexplored the fabrication technology of SAW filter The main results can bedescribed as following:First, we have investigated the deposition of ZnO films on Si(l00), diamondand 6H-SiC substrates Experimental results shows, all ZnO films deposited onthese substrates are well c-axis oriented if the deposition parameters are suitableZnO films are grown with nuclei In certain extent, the rougher the substrate is, thebigger the nuclei density is, and the smaller the root-mean-squared (RMS)roughness of the ZnO film is ZnO films deposited in high vacuum ambient havebetter crystalline but the O in the film is insufficent The crystalline of the ZnOfilms deposited in O₂ ambient is slightly worse, bur the stoichiometry of the filmsis very close to that of ideal ZnO crystal Li⁺ ion has little influence on thereslstlvlt1es of the ZnO films, but the lnfluences of deposlt1on amblent and hlghtemperature anneallng ln pure O: amblent are declslve The reslstlvlty of the ZnOfilm deposlted ln O, amblent or hlgh temperature annealed ln pure O: amblent lslncreased to l07O cmSecond, we deposlted AlN films on Sl(l00) substrate wlth ZnO buffer by PLDExperlmental results show as-deposlted AlN films are c-axls orlented TheAlN/ZnO/Sl(l00) mutll-structure can be seen clearly, and the lnterfaces are verysmooth The use of ZnO buffer can lmprove the roughness of AlN films efficlentlyVery hlgh vacuum or sultable N, amblent ls necessary fOr deposltIng stolchlometrlcAlN filmsFlnally, we explored the fabrlcatlon technology of SAW devlces Our resultsshow that the plezoelectrlc fiIms on substrates are very easy to be damaged ln SAWdev1ce fabr1catlon, and the performance of the SAW devlces IS badly destroyed Sothe technology fOr fabrlcatlng SAW devlces uslng plezoelectrlc slngle crystal cannot be applIed dlrectly ln the fabrlcatlon of SAW devlces us1ng plezoelectrlc thlnfilms...