Untersuchung und Entwicklung von Stromsensorkonzepten für Leistungsbauelemente mit lateralem und vertikalem Stromfluß.

Abstract

A new monolithic integrated high side current sense principle is developed and investigated for power semiconductor devices with lateral and vertical current flow. In such devices the well-known low side sense principles are unsuitable. The special requirements for the integration and the signal processing are discussed in detail. As an example, the new concept is presented with a lateral-vertical transistor (LV-transistor). The load current enters the device on the top of the chip and it is divided to flow to a vertical and lateral main contact. The current distribution in the device depends on the device layout and the operating point. The usual integrated low side current sense principle consists of a current mirror and a sense resistor in the current path. Therefore, only the lateral current component in the LV-transistor could be detected. Especially in the case of turning off the device and simultaneous current control the sense signal will be ambiguous. In the new concept the sense resistor is directly connected to the high voltage side in the load current path, so that the relation between the sense signal and the load current is almost independent of the device parameters. The new current sense concept allows the detection of the current level and makes the current control in a lateral-vertical power switch possible. This is investigated and demonstrated by a test structure of an LV-transistor under ohmic load and an external control system. The temperature and voltage dependence of the sense signal is simulated and measured to define the demands for the subsequent circuitry. For a simple MOS-transistor the results are compared with the behaviour of the low side current sense principle in the case of detecting a current flag. However, it is a disadvantage of the concept, that the sense signal must be transferred from the high voltage side to the low voltage side for further processing. The possibility of signal transfer by monolithic integrated high resistive polysilicon resistors on the RESURF-region is investigated by numeric simulation and measurement. The reactions of the integrated components on the breakdown behaviour of an LV-transistor are simulated and classified as uncritical in respect of the application. The disturbing effects on the sense signal are caused mainly by capacitive coupling between the power device and the high ohmic transfer resistors and determine the critical frequency of the system. Finally, some parasitic influences for the case of current control are analysed and the demands for the processing circuit are discussed. As a result, the fundamental problems of the high side sense principle are investigated for a special LV-device and appropriate solutions are proposed.