A novel micro-electronic strain device fabrication and 2D materials characterization

Abstract

So far strain engineering has proved to be an efficient way to induce and tune the band gap in 2D materials. While mechanical strain device have already been demonstrated, they rely on bending a flexible substrate. However, bending the substrate induces also strain underneath the contacts leading to ambiguities in the interpretation the electrical behaviour of the 2D material and eventually to a complete failure of the contacts. A novel micro-electronic device has therefore been fabricated on thin (200 micron) Si Substrates with silicon dioxide on top of it using optical lithography and deep silicon reactive ion etching, which can create strain in the 2D material (flakes) mounted on it. The idea is to etch a deep trench into the substrate such that the remaining silicon becomes thin enough to act like a hinge. The benefit of this novel device is that there is a rigid substrate underneath the contacts so that strain is only applied in between the contacts. As a result, higher strain levels should be applicable since contact failure due to mechanical strain is avoided. Furthermore, the substrate can be used to get the 2D material within the contact are suppressing the impact of the metal-2D material interface on the measurements. The device was fabricated using microelectronic steps. During the initial phase of fabrication of the device faced few difficulties including the adhesion of thin Photo Resists (AZMIR 701), Silicon Oxide depth, Deep Reactive Etch etc. A new honey Photo-resist was used instead of the thin one and a standard recipe for the new resist was designed. All the ambiguities were overcome successfully and a final fabricated device was tested by giving external strain. The fabrication of the final strain devices provide a flexible strain variation of at least 10-12%. The device can be utilise further to induce strain in two-dimensional layered materials such as TMDCs, which may change the electrical, photonic, phononic and optical properties of those materials by altering the number of layers and changing the band gap.