Temperature Characteristic Analysis Of Polysilicon Structure Components

Polysilicon thin film material has the advantages of simple manufacture, doping controlled, fine process capability. Some devices such as resistance, diode, transistor, and fuse, which are widely used in power devices and power integrated circuit, can be fabricated with this material. The fabricated polysilicon diode has similar temperature property with the bulk silicon, and can be used as temperature sampler for smart power devices with over temperature protection. As this, temperature properties of polysilicon devices (polysilicon diode, polysilicon transistor) is studied in this essay. The polysilicon diode is used for a over temperature smart power device. The study includes these points:1. The electrical characteristic of polysilicon thin film is analyzed. Based on this characteristic, the conductive mechanisms of polysilicon diode and transistor are analyzed and the temperature properties of the two devices are deduced. Then lateral polysilicon diode and transistor are designed with process simulation software. By simulating and analyzing the temperature properties of the two devices, negative temperature coefficient of forward conduction voltage of polysilicon diode is verified and computed value is-1.42mV/℃. Meanwhile, polysilicon transistor has positive temperature coefficient of current gain. The transistor has the same temperature property with bulk silicon with a smaller change of current gain when temperature is varying.2. Polysilicon diode’s function of temperature sampling by using its negative temperature property in over temperature protection circuit is verified and the diode is used in over temperature protection circuit of a smart power VDMOS. The simulations indicate:when input voltage is10V, over temperature protection’s function point is164℃, device’s self recovery point is144℃, sluggish temperature is20℃. Therefore polysilicon diode can be widely used as thermosensitive device in smart power integrated circuit and smart power devices with over temperature protection.