Research On The Fabrication And Electronic Properties Of Monocrystalline Silicon Membrane With Gradient Buckling

Flexible electronics,which aims at achieving stretchable and bendable electronic devices,has drawn much attention of the researchers with the applications in many fields such as healthcare and structural health monitoring.Compared with the organic flexible electronic devices,inorganic flexible electronic devices realized by introducing stretchable mechanical structures are considered to have better performance and higher reliability.Among the typical stretchable mechanical structures,the wavy structure formed by the buckling of the thin film is a simple but widely used one.Moreover,as the wavy structure can be an effective way to introducing the strain with gradient distribution in the thin film,it is also expected to be a potential tool for strain engineering.However,previous studies on the wavy structure formed by inorganic films mainly focused on the regular rectangular ribbons,and the wavy structures formed by irregular rectangular ribbons are rarely reported.Since the change of the width of the ribbon’s shape could lead to the appearance of the non-uniform compress stress in the substrate,the profile of the wavy structure may be affected by the shape of the film.Therefore,the researches on the realization of inorganic semiconductor thin film with gradient wavy structure,and the influences of ribbon’s profile and fabrication parameters on the morphology of the wavy structure,are not only an important part of the studies on the wavy structure in flexible electronics,but propose novel methods to introduce gradient strain in thin films for strain engineering.In this work,the gradient wavy structure is formed by the patterned single crystal Si thin film and its electric properties are studied.After patterning the shape of the film into a symmetrical trapezoidal structure by photolithography and reactive ion etching,the silicon thin film is transferred-printed to the pre-strained elastomeric substrate(PDMS).The film is then buckled to be the gradient wavy structure by releasing the pre-strain of the substrate.The relation between the ribbon’s profile and process parameters is discussed with the morphology data from 3D optical profiler.The strain distribution of gradient wavy structure is also analyzed by theoretical calculation,and the result is then compared to that of the uniform wavy structure.In order to investigate the electrical stability of gradient wavy structure with different external tensile strains,photoelectric properties of gradient wavy silicon film with different external tensile strains are measured and discussed.Finally,a silicon PN junction with gradient wavy structure is fabricated to explore the application of gradient wavy structure in electronic devices.The results indicate that the monocrystalline silicon thin film with gradient wavy structure could be fabricated by the method introduced in this thesis.It is observed that the gradient wavy structure has a gradient distribution of amplitude and wavelength,which leads to the gradient distribution of the strain in the peaks and valleys of the wavy structure.The gradient of distribution of amplitude and wavelength heavily relies on the value of pre-strain,G(a parameter that reflects the shape gradient of the film)and the mechanical property of the substrate.The gradient wavy structure demonstrates a similar deformation ability to the conventional uniform wavy structure.The electrical property of silicon PN junction with gradient wavy structure is stable when a strain of 3.56% is applied,and the transfer process has no effect on the electrical property of silicon PN junction,which shows the potential of this structure in flexible electronics.