Frei applizierbare MOSFET-Sensorfolie zur Dehnungsmessung

摘要

While the integration of semiconductor circuits continues to rise on a fairly high level, the same is not the case regarding package integration. One means of enhancing package integration is using foldable chips. The main requirement for using foldable chips is to manufacture fracture resistent chips without disrupting the functionality of the devices on it. Through the combination of thin chips and flexible polymer substrates, it is possibe to manufacture sensor skins with a high component density which can be applied to three dimensional surfaces. In this dissertation, thin CMOS chips are investigated regarding the fracture toughness as well as the sensitivity of MOSFET inversion channels. The results of the investigations were used for the realization of a MOSFET sensor skin. First, a test chip and a chip for strain sensing were designed under the consideration of existing piezoresistive knowledge. The test chips were subjected to bending experiments in order to extract the piezoresistive coefficients of the inversion channels. Next, the test chips were thinned down to 65 µm and examined concerning their fracture stresses. By careful thinning techniques, tensile stresses exceeding 350 Mpa have been achieved for the first time. Bending experiments with the thinned chips have shown obviously that there is no influence of the thinning on the piezoresistive coefficients. The chips for strain sensing on a sensor skin were thinned down to 10 µm. After the thinning, a reduction of the drain current up to 5% was observed. The chips were mounted on a foldable carrier substrate and connected to the leads. After the attachement on the substrate, a considerable reduction (up to 20%) of the drain current occured. It is assumed that this effect is due to the higher thermal resistance of the sensor skin system. One application of the sensor skin, which has been demonstrated, is to perform torque measurements. The reduction of the shear coefficient of the inversion channels is again assumed to be due the higher thermal resistance of the system as the shear coefficient decreases with temperature.