The piezoresistive mobility modeling for cubic and hexagonal silicon carbide crystals

Abstract

The piezoresistive effect is characterized by the change in the resistivity of a material relative to mechanical forces exerted on it. Such materials can be used as pressure sensors and are among the most important components for micro-electro mechanical system applications. To date, most research on the piezoresistive effect has been directed toward cubic crystalline materials such as Si; however, the prospective non-cubic materials, such as SiC, are known to have exciting and promising properties. SiC exhibits high-temperature robustness and is chemically stable. It is expected that these properties can be applied to a variety of applications. These materials fall in the category of hexagonal crystalline systems, and it is difficult to evaluate the piezoresistive properties of such materials. In this study, we discuss the piezoresistive mobility model that corresponds to both the cubic and the hexagonal crystalline systems. This mobility model is derived from the empirical fitting of the Gauge Factor (GF) values using the longitudinal and the transverse piezoresistive coefficients and the material-unique fitting parameters. Our proposed method has been implemented in the original device simulator and has been evaluated with respect to both Si and SiC materials. This report shows the well-matched GF values and suggests that the proposed piezoresistive effect model can be implemented in device simulation modeling.

High-Temperature Piezoresistance of Silicon Carbide and Gallium Nitride Materials

“…In our previous work, we modeled the piezoresistive effect as the mobility change in our device simulations [6]. The conventional piezoresistive model, which is mainly applicable to cubic crystal materials, is based on the piezoresistive coefficient tensor components π 11 , π 12 , and π 44 , which reflect the mobility enhancement [7].…”

“…To evaluate the piezoresistive effect, we determine the stressed mobility µ P iezo l,t using the non-stressed mobility µ 0 , the longitudinal and transverse piezoresistive coefficients, and stresses. To increase the accuracy of estimation, we consider the unique modification factor of the material, which exhibits a piezoresistive-coefficient dependency [6]. Thus, we have…”

“…In addition, the resistance change of the piezoresistor was calculated as the difference between the resistance under the final strain condition and that under the thermal expansion strain condition (no external force). In our study, the electrical simulation was performed with the use of our original device simulator, called SeMS [6], and was customized for evaluating piezoresistor performance. Subsequently, in the simulation, a voltage bias of 1 V → -1 V was applied to obtain the I-V characteristics.…”

“…In particular, SiC materials exhibit a significant high-temperature robustness, withstanding temperatures of over 600 • C. With regard to the application perspective, it is particularly important to understand the physics of the material under high temperatures; in this regard, some studies have focused on the temperature dependences of the piezoresistive coefficients of SiC and GaN, with experiments estimating the GF values in lieu of the piezoresistivity performance [4], [5]. Meanwhile, with regard to numerical simulations, the piezoresistive coefficient plays an important role in the evaluation of the piezoresistive effect, and in a previous work, we proposed piezoresistive mobility modeling using the longitudinal-and transverse-direction piezoresistive coefficients [6]. Based on the above study, we note that to evaluate the piezoresistive effect at high temperatures, the input piezoresistive coefficients should be modified; thus, the temperature dependence of these coefficients plays a significant part in the evaluation.…”

Modeling and Analysis of a SiC Microstructure-Based Capacitive Micro-Accelerometer

“…The wide band-gap and high thermal stability of SiC allow certain types of devices to operate indefinitely at junction temperatures of 300 °C or higher without measurable performance degradation. The potential markets for SiC sensors include the Radio Frequency (RF) MEMS [ 39 ], the pressure sensors used in the petroleum industry [ 40 ], the acceleration sensors in aircraft engines and motors [ 41 ], and the optical MEMS [ 42 ].…”