Controlling the intrinsic bending of hetero-epitaxial silicon carbide micro-cantilevers

Abstract

We introduce a simple methodology to predict and tailor the intrinsic bending of a cantilever made of a single thin film of hetero-epitaxial silicon carbide grown on silicon. The combination of our novel method for the depth profiling of residual stress with a few nm resolution with finite element modelling allows for the prediction of the bending behaviour with great accuracy. We also demonstrate experimentally that a silicon carbide cantilever made of one distinct film type can be engineered to obtain the desired degree of either upward, flat, or downward bending, by selecting the appropriate thickness and cantilever geometry. A precise control of cantilever bending is crucial for MEMS applications such as micro-actuators, micro-switches, and resonant sensors. I. INTRODUCTION Epitaxial cubic silicon carbide (3C-SiC) is a leading material for micro electrical mechanical systems (MEMS) due to its excellent mechanical properties when silicon (Si) has limitations. 1-4 Furthermore, it can be grown on Si substrate which results in large area, easy micromachining, and low cost production.

Engineering Stress in Thin Films: An Innovative Pathway Toward 3D Micro and Nanosystems

“…[200] Another approach is the use of multiple layers with a variation of thermal stress [197,198,201,202] or epitaxial stress. [203][204][205][206] The bending angles and directions can be engineered by inducing a tensile or compressive stress in each layer from the growth process [200,207] The residual stress technique has been applied in various materials such as SiC, [199] SiN, [208][209][210] SiO x , [198,202] and AlN. [197,211] Figure 6a shows a typical procedure for fabrication of a standing piezoresistive cantilever, [197] which can be generalized for all types of out-of-plane structures.…”

“…Copyright 2011, Elsevier; d) SEM images SiC curved cantilevers with different thickness. Reproduced with permission [199]. Copyright 2015, AIP Publishing.…”

Factors affecting the f × Q product of 3C-SiC microstrings: What is the upper limit for sensitivity?

“…The quality of thin heteroepitaxial SiC on silicon films is notoriously hindered by an extensive amount of crystal defects due to the large lattice mismatch of the system, and we reported previously that our SiC(100) films have an overall better crystal quality than SiC(111) films, thanks to a faster stress relaxation rate. 64,74 It is therefore expected that SiC(100) film would have a smaller component of defect-driven energy dissipation. Therefore, the effect of the mean stress is compensated by the influence of the film quality, resulting in the comparable Q factors.…”