Fabrication Of Ultra-high Sensitivity SAW Device Based On Electron Beam Lithography Processing

Surface acoustic wave(SAW)devices have a very wide range of applications including quantum communication,filters in radio-frequency communication,micro-sensors for detecting physical parameters and biochemical substances,microfluidics and lab-on-a-chips.For most SAW applications(except for microfluidics),there is a strong demand to achieve super-high frequency devices.This is because high frequency devices have many irreplaceable advantages,for example,to enhance processing speed for significantly increased volume of information in data transmission systems,to reach the quantum regime,or to improve the sensitivity of sensor.This paper reports a nano-patterning process for achieving an extremely high frequency of surface acoustic wave(SAW)device with a super-high mass sensitivity.An integrated lift-off process with ion beam milling is used to minimize short-circuiting problem and improve quality of nanoscale interdigital transducer s(IDTs).A specifically designed PEC algorithm is applied to mitigate the proximity effect occurring in the electron-beam lithography process.The IDTs with a period of160 nm and a finger width of 35 nm are achieved,enabling a frequency of?30 GHz on lithium niobate based super-high SAW devices.Analyzed and compared the possible problems and micro-machining techniques in the manufacturing process of super high frequency SAW devices,and successfully prepared IDT on a variety of substrates of lithium niobate,lithium tantalate,silicon wafers,Al N/diamond.Using finite element simulation and theoretical calculations,the data accuracy and scientificity of the super-high frequency SAW device were verified.Both centrosymmetric type and axisymmetric type IDT structures are fabricated on lithium niobate and results show that the centrosymmetric type tends to excite lower-order Rayleigh waves,and the axisymmetric type tends to excite higher-order wave modes.Super-high mass sensitivity of?388.2 MHz mm~2/?g is demonstrated,which is~10~9 times larger than that of a conventional quartz crystal balance and ?50 times higher than a conventional SAW device with a wavelength of 4?m.