Design,Fabrication And Applications For High Frequency Surface Acoustic Wave Devices Based On Layered Structure

Surface acoustic wave(SAW)devices is an important component in numerous applications,such as wireless communication,radio frequency tag,sensor detection,quantum research and other fields,due to their low loss,small volume and real-time signal processing.However,with the coming era of 5G and Internet of Things,increasing the resonant frequency of SAW devices is essential.It limits SAW device applications by conventional lithographic techniques and weak output power.In this paper,design and fabrication of high-frequency SAW devices with layered structure is focused on.Based on a theme of “device design,nano-electrode fabrication,performance optimization”,SAW devices in high-frequency range are studied,and five aspects are shown as follow:1.Based on transfer matrix model and finite element model,AlN/diamond/Si layered structure with high acoustic velocity is designed and the material is fabricated.Firstly,based on transfer matrix model,the SAW propagation characteristics in AlN/diamond/Si layerd structure are calculated,including phase velocity characteristics and electromechanical coupling coefficient characteristics,of 1-5 order Rayleigh wave.It is found that to obtain superb performance,the normalized thickness should be 1 ? 3 and the devices should work in Sezawa mode.Secondly,using the finite element model,it is found that the gold electrode can obtain highest SAW resonant frequency in nanometer scale during three metal materials,due to its highest acoustic impedance.Thirdly,AlN/diamond/Si and AlScN/diamond/Si layered structures are fabricated.The result show that two materials are highly c-axis oriented with surface roughness less than 5 nm,which is suitable for application of high-frequency SAW devices.2.SELSP method is proposed in this paper combined with the interdigital transducer(IDT)characteristics of multiscale patterns,aiming at low yield of high-frequency IDT by electron beam lithography.Compared with the traditional electron beam lithography process,it is found that SELSP method not only has advantages in preparing high-resolution dense structure,but also has high fidelity in fabircation,and has universality for different feature sizes in tens nanometers.Based on this method,a SAW resonator based on electrical excitation was fabricated for the first time in the Ka-band.3.The embedded IDT is also proposed in this paper to effectively improve the resonant frequency and output power of high-frequency SAW device.Based on the same AlN/diamond/Si layered structure,SAW resonant frequency and output power excited by the embedded and conventional electrodes respectively were compared by the finite element method and experiment.It is found that the output SAW power and resonant frequency of Sezawa modes are improved in the high frequency band,for the embedded IDT devices.And this is because the different field distribution leads to the different Bragg reflection and phase velocity for the two types of IDTs through data comparison and analysis.4.SAW resonator based on AlScN/diamond/Si layered structure are designed,fabricated and tested for the first time in this paper as well.It is found that with the increase of resonant frequency,the high-order modes of Rayleigh wave become the dominate modes,making high-order Rayleigh wave can be observed,which makes the AlScN/diamond/Si substrate have higher frequency advantages than the AlN/diamond/Si substrate.It provides a new approach for high-frequency SAW device design.5.High-frequency SAW applications on biosesing field and on-chip radar are feasibility studied.High-frequency SAW devices have advantages in the field of sensors.For the development of VHF,ultra-high-precision Researching on the relationship between solution concentration and reusability of single-port SAW sensors based on LiTaO3 substrate,it is found that the device has the ability to distinguish small mass,and the frequency drift is exponential with the solution concentration.These results are consistent with the theoretical expression and has good reusability demonstrating that SAW devices have the potential to achieve high-precision sensors.In addition,for the on-chip millimeter wave radar exploration,a radar receiving link based on SAW pulse pressure signal processing is proposed,to alleviate the computational pressure of digital signal processor when processing a large number of signals.The SAW pulse compressor was fabricated based on LiNbO3 and the SIP package was designed and completed.The test results show that the link output signal meets the design expectations,which demonstrates the feasibility of the signal processing link.