Back Gate Effects in N-Channel Monocrystalline Silicon Devices-on-Glass and their Suppression by Boron Ion Implantation

Abstract

Initial N-channel self aligned polycrystalline silicon gate transistors fabricated on 1.5μm -2μm single crystal Silicon-O-Glass(SOG) layers exhibited poor transfer characteristics. Measured threshold voltages and On/Off current ratios were in the order of -8V and 10 respectively. This is due to the presence of fixed charge at the bond interface introducing back gate effects which degrade and distort device performance. These back gate effects were suppressed by implantation of boron into the silicon substrate prior to oxidation and bonding, with energy 40keV and dose 7.4×1012cm−2. This resulted in an improvement in device performance with a threshold voltage of-0.54V. On/Off current ratio increased to 1840 and field effect mobility increased from 274cm2/Vs to 357cm2 Vs