Semiconductors such as Si or GaN are rigid in nature and are not intrinsically stretchable. To render materials stretchable, device layers must be both sufficiently thin (~ 1 – 5 µm) and attached to stretchable substrates such as silicone. In addition, devices must have unique stretchable geometries such as a sinusoidal or horseshoe shape to relieve strain and prevent breakage. In this work, we have theoretically modeled the effects of device geometry on the mechanical properties of both GaN and Si using COMSOL finite element solver for the Hooke’s Law equation for continuous media using published values of the stiffness matrix and mass density of both Si [5] and GaN [6]. We examined straight, sinusoidal, horseshoe, rectangular and curve corner rectangular (CC-rectangular) device geometries for both materials with Sylgard 184 (Dow Corning) as a stretchable substrate [7]. Figure 2 shows our results with peak stress plotted as a function of peak to peak amplitude for multiple device geometries. Our results show that the peak stress for multiple device designs in GaN material is approximately 2.5 times larger than that of Si which can be attributed to the difference in Young’s Modulus and thus components of the stiffness tensor between the two materials. Because Si based devices have been rendered stretchable, our mechanical simulations suggest that GaN based devices such as the HEMT are also potential candidates for stretchable electronics.
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