Low-Energy Dissipation Diamond MEMS

Abstract

Microelectromechanical systems (MEMS) that integrate tiny mechanical devices with electronics on a semiconductor substate have experienced explosive growth over the past decades. MEMS have a range of wide applications from accelerometers and gyroscopes in automotive safety, to precise reference oscillators in consumer electrons to probes in atomic force microscopy and sensors for gravitational wave detection. The quality (Q)-factor is a fundamental parameter of a MEMS resonator that determines the sensitivity, noise level, energy efficiency, and stability of the device. MEMS with low energy dissipation have always been pursued. Despite the brilliant progress of silicon-based MEMS due to the mature technology in counterpart microelectronics, the intrinsic material properties limit the sensitivity and reliability, especially for the applications under extreme conditions. Diamond has emerged as the ideal semiconductor material for low-energy dissipation MEMS with high performance and high reliability, owing to its unparalleled material properties, such as extremely high mechanical strength, superelectrical properties, highest thermal conductivity, and chemical inertness. Diamond resonators are thus expected to exhibit high Q-factors, and high reliability, with low thermomechanical force noise and long coherence rate of mechanical quantum states, not only improving the performance of MEMS devices but also expanding to the quantum domain. Single-crystal diamond (SCD) is desirable to achieve the ultralow energy loss or high Q-factor MEMS resonator due to the nonexistence of grain boundaries and other carbon phases. However, micromachining for SCD is tough and heteroepitaxial growth of SCD on foreign substrates remains quite difficult.

In this Account, we provide an overview of the recent research and strategies in SCD diamond MEMS for achieving high Q-factors, focusing on those fabricated by the smart-cut method developed in our lab. We start with the concept of diamond MEMS, covering structure fabrication, fundamentals, and applications. A comprehensive discussion of the energy dissipation mechanisms on the Q-factors in diamond MEMS resonators is provided. The approaches to enhance the Q-factor of diamond resonators including (1) the growth of high crystal quality SCD epilayer on the ion-implanted substrate, (2) defects engineering, and (3) strain engineering by thinning the resonator to around 100 nm thick are presented. In the smart-cut method, the ∼100 nm thick defective layer contributes to the main intrinsic energy loss. By combing the growth of a high crystal quality diamond epilayer above the defective layer and the atomic scale etching of the defective layer, the Q-factors could be improved from thousands to over one million at room temperature, the highest among all the semiconductors. The intrinsic high Q-factors of SCD MEMS are also due to the well-controlled purity of the diamond epilayer and the ultrawide bandgap energy of diamond. Through strain engineering of the SCD MEMS beam to nanoscale, the Q-factor is expected to be further enhanced. These strategies represent pivotal steps in advancing the performance and applicability of diamond MEMS resonators.