1. Ultra Thin Body SOI FETs SINDHU REDDY ALLA

2. Introduction SOI uses Silicon On Silicon insulator instead of Si substrate SOI is used to reduce parasitic device capacitance which improves the performance The choice of insulator can be varied depending on the requirement Cross Section of ultra thin body SO 3. Benefits of SOI Technology Lower parasitic capacitance Resistance to latch up Higher performance at equivalent VDD Reduced temperature dependency Better yield due to high density Reduced antenna issues No body or well taps are needed Lower leakage currents Radiation hardened thus reducing the need for redundancy 4. Types of SOIs Partially Depleted SOI Fully Depleted SOI Of these Fully Depleted Silicon On Insulator is preferred because of its thin size, reduced leakage current and improved power consumption characteristics 5. Difference between FDSOI and PDSOI PDSOI FDSOI Insulating BOX thickness is 100 to 200nm Insulating BOX thickness is 5 to 50nm Top silicon layer 50 to 90nm Top silicon 5 to 20nm Used in analog circuit Low power applications Easy to manufacture Leakage and power consumption reduced drastically Drawback: packaging scalability Drawback: complex fabrication process 6. Electrical Behavior SOI MOSFETs are prone to self heating as the thermal conductivity of SiO layer is lower than the silicon layer There are two factors that are to be considered for the analysis of electrical characteristic for an UTB SOI The inversion electron- channel thickness of an MOSFET is less than 10nm If the top silicon layer is thinner than the inversion layer, the channel thickness is determined by the decrease in the top silicon layer thickness UTB SOI MOSFETs suffer from interfacial roughness and top silicon layer thickness 7. Leakage Current Path Leakage current path for MOSFETs Leakage current path for SOI MOSFETs 8. Leakage current in SOI MOSFETs Leakage current Vs. Operating tempera The leakage current of 8.5nm thick UTB depends strongly on the temperature than the 4.5nm The leakage current increment of the slope of 8.5nm thick UTB SOI is 2.6 times steeper than for a 4.5nm thick SOI 9. Threshold voltage vs. operating temperature The figure shows the threshold voltage as a function of operating temperature for various thickness of Si The relation between VT and temperature is given by 10. Advantages of thin body SOIs Improved transistor subthreshold swing due to greatly improved gate control, Improved channel mobility due to reduced transverse electric field, Reduced parasitic capacitances from the absence of depletion capacitances, leading to improved speed, and Reduced power consumption 11. Applications The buried oxide layer can be used in SRAM memory Used in micro electronics industry In high performance radio frequency applications Used in photonics