With the development of wireless communication from 5G to Beyond 5G (B5G) and 6G, there is still an international debate on the use of electromagnetic spectrum above 6 GHz, some countries have authorized the 6 GHz full band for Wi-Fi 6E, and more countries are considering using this band for cellular wireless communication (6G). Therefore, due to the need for the isolation of signals between different standards and frequency bands, the high-quality factor (Q value) acoustic resonator and high-performance filter working at 6 GHz will become the key technology for the development of wireless communication in the next stage, and it is also the basic RF components and chips that must be autonomous and controllable for the development of 6G technology in China.

Recently, the research team of Professor Zuo Chengjie of the School of Microelectronics of the University of Science and Technology of China has designed and implemented a high-frequency (6.5 GHz) MEMS resonator with a Q value of more than 100,000 on a lithium niobate (LiNbO3) piezoelectric film, which has improved the Q value by 2 orders of magnitude compared with the existing work in the literature. The results were published online on May 16 in IEEE under the title of "Ultra HighQLithium Niobate Resonator at 15-Degree Three-Dimensional Euler Angle" Electron Device Letters.

A method for designing and fabricating high-frequency MEMS resonators on x-cut single-crystal lithium niobate piezoelectric films based on three-dimensional Euler Angle α is proposed. By designing the electrode structure of the resonator, the S1 vibration mode operating at 6.5 GHz is excited, and when the sound wave propagation direction (α) is 15°, the quality factor (Qp) at the parallel resonant frequency (fp) of the resonator is as high as 131540. The corresponding resonator values k2·Qp and fp·Qp reached 6300 and 8.6×1014Hz respectively (Figure 1).

Figure 1. Structural design and performance test of the new MEMS resonator: (a) Definition of three-dimensional Euler Angle; (b) SEM photos of the prepared resonator; (c) Test result of admittance curve of 15° resonator

As shown in Figure 2, compared with other resonators working in similar frequency bands in the past 10 years, the new MEMS resonator improves the Q value by 2 orders of magnitude, and for the first time breaks through the resonator optimal limit that is difficult to improve synchronously by the product of the resonant frequency and Q value (f·Q). More importantly, the relevant work successfully found a new mechanism that can regulate the dielectric loss and acoustic loss of lithium niobate thin films by using three-dimensional euler Angle, opening up more possibilities for future micro and nano devices in applications such as high-frequency wireless communication, medical ultrasound imaging, intelligent information processing and Internet of Things sensors.

Figure 2. Comparison of Q values of new MEMS resonators with other lithium niobate resonators in the past 10 years

Professor Zuo Chengjie of the School of Microelectronics of the University of Science and Technology of China is the corresponding author of the paper, and Dai Zhongbin of the School of Microelectronics is the first author. The research work was supported by the National key Research and development Program and the Central University Basic Research Fund, as well as by the School of Microelectronics of the University of Science and Technology of China, the Micro and Nano Research and Manufacturing Center of the University of Science and Technology of China, the Institute of Advanced Technology of the University of Science and Technology, and the Key Laboratory of Wireless Optoelectronic Communication of the Chinese Academy of Sciences.

Paper link:

https://doi.org/10.1109/LED.2022.3175572

(School of Microelectronics, School of Information Science and Technology, Department of Scientific Research, University of Science and Technology of China)
Source: HKUST News Network