Stiction Fault in MEMS Comb Drive Resonator Bhushan Dharmadhikari 1 , Sarosh H Patel 2 and Tarek Sobh 2 Abstract - MEMS devices are vulnerable to various defect sources, such as point stiction, broken-beams, etch variation. Point stiction is the defect in which the movable parts of the device is stuck to the substrate or fixed parts at one or multiple point locations. Point stictions may affect the yield as well as the reliability of MEMS devices. Fault simulation is an effective way to study how the point stiction defects will affect the device yield and reliability. For point stiction defects, the occurrence and the location are random and cannot be precisely predicted. Such stochastic behavior can be better predicted with the Monte Carlo simulation. Monte Carlo simulation is a stochastic technique used to approximate the probability of specific outcomes by running multiple trial simulations using random numbers and probability statistics. In this paper, the ANSYS Monte Carlo simulation is used to simulate point-stiction defects in surface-micromachined MEMS comb resonator devices. The yield of MEMS devices is estimated based on the simulation results. The fault simulation in MEMS devices is essential to optimize the device performance and to improve the yield and reliability of MEMS devices Index Terms — MEMS, Resonator, Point Stiction, Monte Carlo simulation. I. INTRODUCTION MEMS devices have been widely used for many applications due to their small size, low cost, low energy consumption and high resolution [1]. However, most MEMS devices involve movable parts, and they are diverse in device structure and working principles [2]. As a result, they are vulnerable to many more defect sources compared to their VLSI counterparts. As an example, point stiction defect is a popular failure mechanism for MEMS [3, 4]. Further, how to improve the yield of MEMS is an essential issue for MEMS commercialization. Up to now, a well- developed MEMS yield model is not available yet [5]. How to estimate the yield of MEMS remains a challenging issue. In this paper, we utilized Monte Carlo simulation of point stiction to estimate the yield of MEMS comb resonator and investigate how the random point stiction defects affect the MEMS device behavior. A typical surface-micromachined poly-silicon MEMS comb resonator device is shown in Fig. 1A The four folded beams are connected to two anchor points, which are fixed to the substrate [6]. The left and right fixed comb fingers consist of parallel plate capacitances with movable fingers. The resonator is activated with electrostatic push-pull driving [7]. 1 Bhushan Dharmadhikari is with the Department of Electrical and Computer Engineering & Technology, Minnesota State University, Mankato, MN-56001, USA (corresponding author: bhushan.dharmadhikari@mnsu.edu) 2 Sarosh Patel is with. Department of Computer Science & Engineering, University of Bridgeport, CT-06604, USA; email - saroshp@bridgeport.edu, 2 Tarek Sobh is with Department of Computer Science & Engineering, University of Bridgeport, CT-06604, USA; email – sobh@bridgeport.edu Fig. 3B shows a schematic of the simplified lateral folded flexure comb drive resonator. The electro-mechanical mixed domain is presented as an interconnected set of lumped- parameter components, shuttle mass, two folded flexure springs and pair of comb finger actuators represented by two variable capacitors. The combination of these components serves both electrical as well as mechanical roles in the device. The voltage source that power up one actuator is displayed by V [8] The comb resonator has been widely used in MEMS activation and RF communications. The resonator can be viewed as a spring-mass-damper system, where the damping is caused by the air surrounding the movable parts, which include the shuttle mass, movable comb fingers, and spring beams [9]. The air gaps between the fixed and movable fingers form capacitors when a potential difference is applied between the fixed and movable fingers. By applying a voltage across the fixed and movable fingers of the upper comb drive, an electrostatic force of attraction is produced [10]. Fig. 1. (A) Layout of MEMS lateral folded flexural beams comb drive resonator model (B) Mixed-domain schematic of the lateral folded-flexure comb-drive microresonator, including a voltage source, V, for comb-drive actuation [8]. In typical operation, driving voltages Vfu and Vfd, the driving voltages are applied to the top and fixed bottom fingers, 888 978-1-7281-5169-4/20/$31.00 c 2020 IEEE Authorized licensed use limited to: Lawrence Tech University. Downloaded on June 14,2021 at 16:33:26 UTC from IEEE Xplore. Restrictions apply.