A new type of ultraviolet (UV) light sensor based on film bulk acoustic wave resonator (FBAR) is proposed. The new sensor uses gold and a thin n-type ZnO layer deposited on the top of piezoelectric layer of FBAR to form a Schottky barrier. The Schottky barrier's capacitance can be changed with UV light, resulting in an enhanced shift in the entire FBAR's resonant frequency. The fabricated UV sensor has a 50 nm thick n-ZnO semiconductor layer with a carrier concentration of ~ 1017 cm−3. A large frequency downshift is observed when UV light irradiates the FBAR. With 365 nm UV light of intensity 1.7 mW/cm2, the FBAR with n-ZnO/Au Schottky diode has 250 kHz frequency downshift, much larger than the 60 kHz frequency downshift in a conventional FBAR without the n-ZnO layer. The shift in the new FBAR's resonant frequency is due to the junction formed between Au and n-ZnO semiconductor and its properties changes with UV light. The experimental results are in agreement with the theoretical analysis using an equivalent circuit model of the new FBAR structure.

Human skin contains multiple receptors, and is able to sense various stimuli such as temperature, pressure, force, corrosion etc, and to feel pains and the shape of objects. The development of skin-like sensors capable of sensing these stimuli is of great importance for various applications such as robots, touch detection, temperature monitoring, strain gauges etc. Great efforts have been made to develop high performance skin-like sensors, but they are far from perfect and much inferior to human skin as most of them can only sense one stimulus with focus on pressure (strain) or temperature, and are unable to visualize sensations and shape of objects. Here we report a skin-like sensor which imitates real skin with multiple receptors, and a new concept of pain sensation. The sensor with very high resolution not only has multiple sensations for touch, pressure, temperature, but also is able to sense various pains and reproduce the three dimensional shape of an object in contact.

An electrically tunable Au/N-ZnO/ZnO/Al film bulk acoustic resonator (FBAR) is proposed. The stack resonator is Au-piezoelectric ZnO layer-Al while Schottky diode junction is Au/N-ZnO semiconductor layer. The FBAR's resonance frequency changes as the junction capacitance decreases with reverse bias. Our experiments gave a frequency shift of ∼30 kHz/V at 1.46 GHz, maximum insertion loss ∼0.7 dB, and a very high Q factor above 1200. Circuit simulations indicated a tunable range of ∼3.8 MHz from optimizing the FBAR's structure and doping concentration of N-ZnO. Electrical tunability decreases from 27 kHz/V to 1.5 kHz/V with temperatures from 30 °C to 105 °C.

A novel flexible Film Bulk Acoustic Wave Resonators (FBARs) based on ZnO/PET structure was fabricated without back-etch. The PET layer is applied as acoustic reflector and substrate of FBAR. It has 1.14GHz parallel resonant frequency, 1.229GHz series resonant frequency and about 150 Q factors. The FBARs acoustic impedance is improved by using harden metal Au instead of AI as the bottom electrodes. TheZnO/PET structure FBAR is also simulated by COSMOL to confirm its working mechanism.