The Design Of A CBSLOP LDMOS With Floating Source SENSE FET Device

It is essential to improve the contradictory relationship between the breakdownvoltage and the specific on-resistance of power devices, which are the key componentsof power management ICs. Finger lateral high voltage MOSFETs, the most popular typeof power devices, always have an earlier breakdown occurred at the fingertips of thesource side than other places because of the lateral curve effect from the corner of themask. Besides, SENSE FETs are often used in analog system to perform currentdetection, over current protection and current mode control. While it is difficult to makethe source of the detection device be floating, which may lead to an inaccurate result.Therefore, this thesis focuses on two devices. One is an LDMOS with a highbreakdown voltage and a low specific on-resistance, and the other is a SENSE FETwhose source is floating. The main content of this thesis is as follows:(1) Make a research on CBSLOP LDMOS. First introduce CBSLOP structure toimprove the contradictory relationship between the breakdown voltage and the specificon-resistance. Then analyze the influence of parameters on the breakdown voltage andthe specific on-resistance. These parameters include the concentration of drift region,the dose of P/N columns and charge balance.(2) Solve the problem of lateral curve effect. Apply the substrate terminationtechnology on the fingertips of the source side to expand the curvature radius, whichcan effectively release curve effect. Make use of the TCAD software tool Silvaco tosimulate the effects on the breakdown voltage caused by the length of the P-body andthe parameters of the substrate termination in the cylindrical coordinate system.(3) Make a research on the floating of the source side of the detection device.Ensure the detection resistance be independent of the substrate resistance to obtain adevice whose source voltage can be floating without any change of breakdown voltageand threshold voltage on the main device.(4) Develop a corresponding process and layout. And the experiment result showsthat an800V device with a specific on-resistance180m·cm~2is obtained.