Tunable SAW Devices Based on Ni:ZnO/ZnO/GaN Structures with Buried IDTs

Abstract

Tunable RF devices have promising applications in low-power resettable sensors, adaptive signal processing, and secure wireless communications. We report a tunable surface acoustic wave (SAW) device built on a multifunctional ZnO/GaN-based structure. The device consists of a piezoelectric Ni:ZnO (NZO) layer deposited on the top of a ZnO/GaN semiconductor heterostructure. The multifunctional ZnO layers are made through a hybrid deposition technique: RF sputtering of a piezoelectric NZO layer and metallorganic chemical vapor deposition (MOCVD) of a semiconducting n-type ZnO layer on the GaN/Al 2 O 3 substrate. This multifunctional and multilayer structure combines the large electromechanical coupling coefficient of ZnO and high acoustic velocities of GaN. The unique dispersion relationship in ZnO/GaN enables high-frequency (GHz) operation using higher order SAW modes. Two device configurations are designed: one with the interdigital transducer (IDT) exposed on the NZO surface, and one with the IDT buried inside NZO layer. Both devices operate at the GHz frequency. SAW frequency tuning is achieved by voltage controlled acoustoelectric interaction. The device using the buried IDT structure has better performance over the counterpart with exposed IDT SAW. The ZnO/GaN-based tunable SAW device with buried IDTs operating at 1.35 GHz has frequency tunability of Surface acoustic wave (SAW) devices are commonly used in communication and signal processing.1 Recently, SAW devices are also employed in wide area network, wireless local area network communications, wireless passive identifications tags, 2,3 various sensors, 4-6 and RF front-end for mobile communications. 7,8 In a conventional SAW device, SAW frequency is determined by the acoustic velocity of the substrate material, and the acoustic wavelength determined by the IDT design. Therefore, it has a fixed operating frequency without agility. However, many modern communication systems require multi-band and multi-mode capability for signal transmitting and receiving. With increasing demands for advanced wireless communication, such as IoT (Internet of Things), it is not practical to simply add more filters. Frequency tunable devices, such as adaptive filters, can process multi-channel signals, extend the operating bandwidth, and reduce the architecture complexity. Furthermore, tunability in the time or frequency response domain allows a reconfigurable system to smartly adapt to its operating environment.Tunable SAW devices are usually achieved through three different approaches: wavelength selection, perturbation of piezoelectric material properties, and perturbation of SAW boundary conditions. Wavelength selection is often referred as a filter bank, which provides frequency variations through switching between selectable IDTs. However, such "tuning" is not continuous due to the discrete switching among filters. Furthermore, the resulting large device area essentially excludes its applications in compact mobile systems. The perturbation of piezoelectric material proper...

Tunable surface acoustic wave device using semiconducting MgZnO and piezoelectric NiZnO dual-layer structure on glass

“…For comparison, two types of channel are deposited on SiO 2 dielectric layer: (i) a layer of 40 nm Mg 0.03 Zn 0.97 O (MZO) forming a SiO 2 /MZO interface structure (regular MZO), and (ii) an identical 40 nm MZO layer with the interface modification using 5 nm MgO, comprising a SiO 2 /MgO/MZO interface structure (m-MZO). After that, a 1.6 μm thick piezoelectric NZO layer was deposited using RF sputtering (5 at% Ni in ZnO target) to form the SAW device with IDTs buried underneath the NZO piezoelectric layer to reduce energy loss and increase SAW coupling [35], as shown in figure 1(c). There are 20.5 pairs of the electrode for each IDT with a period (P) of 8 μm.…”

Modeling and Optimization of CMOS Compatible Various ZnO/SiO2/Si Multilayer Structure for SAW Devices Using FEM

“…The SAW device with a multilayer structure creates new development opportunities because of its unique combined properties such as high frequency of operation, high electromechanical coupling coefficient, improve stability, and low-temperature coefficients, which do not appear for bulk materials [22]. With multilayered structures, materials are combining with different properties in one stack can satisfy the requirements of low losses, size reduction, and high quality saw the device [23].…”