A Gradient Doped Integrated JFET With Improved Current Capability for HV Start-Up Circuit

The conventional high-voltage (HV) JFET (C-JFET) for HV start-up circuit suffers space charge modulation (SCM) effect especially when high current capability is required. Thus, the trade-off relationship between on-state breakdown voltage (ON-BV) and saturation current (I
_Dsat
) is worthy of analysis. In this work, a gradient doped integrated HV junction field effect transistor (JFET) for HV start-up circuit with high ON-BV and high I
_Dsat
is proposed. In the resistance region and drift region of the proposed JFET, different slot ratios of deep N-well (DNW) are adopted. Hence, the gradient doped drift region with adjusted injected current and concentration enhanced N-buffer region can be obtained without adding extra mask. Benefit by introducing the gradient doped structure, the dose of DNW can increase. The well- calibrated simulated results indicate that the proposed HV JFET with
$147~\mu $
m device length can obtain 889 V ON-BV and 929 V OFF-BV with 0.152 mA/
$\mu $
m current capability, which is 21.6% better than our previously proposed D-JFET at the same off-state breakdown voltage level with the same device length.