On-chip Acoustic-driven FETs And Sensors Based On Piezoelectric MEMS Resonators

Piezoelectric resonators are widely used in electronic devices.As consumers'needs increase,resonators'functions also need to be diversified and optimized.One way to meet such need is to apply the more-than-Moore technology,i.e.device performance can be improved and diversified without size increase.An effective approach is to monolichically integrate resonators with other structures.Since the fabrication process of piezoelectric Micro-Electro-Mechanical System?MEMS?resonators are highly compatible with Complementary Metal Oxide Semiconductor?CMOS?technology,it greatly facilitates integrating various structures with the resonators to diversify and optimize their functions.In this dissertation,we explored a monolithic integration technology,and applied it to integrate MEMS resonators with other structures.The integrated device exhibits improved performance and this integration technology makes a good example for the more-than-Moore concept.On the one hand,we monolithically integrate a resonator with a graphene field effect transistor?FET?.The two device not only can work independently,but also coherently.Due to the acousto-electric?AE?effect,the graphene FET can be driven by the acoustic wave excited by the resonator.Compared with a conventional graphene FET,the acoustic-driven FET exhibits a higher on-off ratio.Three kinds of resonators are developed,including a surface acoustic wave?SAW?resonator based on aluminum nitride?AlN?and silicon,a Lamb wave resonator?LWR?based on AlN and silicon,and a SAW resonator based on lithium niobate?LiNbO₃?thin film and silicon.All the three kinds of resonators are monolithically integrated with graphene FETs,and succeed in exciting AE current in graphene.The device based on AlN SAW is the first one to realize AE current modulation by an integrated gate electrode.The device based on AlN LWR excites an AE current at 2.9 GHz,which is the highest frequency that can induce an AE curret.Compared to the two devices,the device with lithium niobate?LiNbO₃?thin film shows a higher AE current and it has great potential to be a new type of graphene FET that can be completely swithed off.On the other hand,a micro channel made of AlN is monolithically integrated with a film bulk acoustic resonator?FBAR?.The channel prevents acoustic dissipation and contributes to a high Q factor in liquid phase.The FBAR sensor exhibits a frequency and Q product of 1.1×10¹²,which is the highest value among all the piezoelectric resonators working in liquid.The high-Q FBAR sensor is used to monitor liquid concentration in real-time.