Electrothermal Modelling of SOI MOSFETs

Fig.l shows the structure of a normal SOI M O S F E T. The device is built in a silicon island. Ex-cept the contacts the silicon island is surrounded by silicon dioxide, thus the device is insulated electrically. Just such insulation results in the possibility of very high packing density. At the same time it is also thermally insulated owing to the poor thermal conductivity of silicon dioxide. Therefore there is a rather large thermal resistance in SOI M0SFETs [ l,2]. This thermal resistance leads to the fact that the channel temperature is higher than that of surroundings; namely the channel area will be heated. The channel temperature increase will greatly change device electrical properties, and conversely the electrical property change will also alter the temperature increase. At the stationary state therefore the device has a certain increased temperature and dissipated power which are coupled together and influenced by each other. Thus the electrical properties of SOI MOSFETs are not only determined by device electrical parameters but also by device thermal parameters, and the modelling of device is no longer only an electrical process but should also be a electrothermal coupling process. We use the following equations as physically basic modelling principle