Smart-power solenoid driver for 300°C operation

A 28 volt solenoid driver has been realized in partially-depleted SOI CMOS technology. The design features an n-channel high voltage MOSFET with an extended drain and a polysilicon field plate, and an on-board flyback diode, each capable of sinking 0.5 A of current and dissipating about 1 W of DC power. Pulse-width modulation (PWM) control maintains low dynamic power dissipation in the drive FET, while the externally selectable “pull-in and hold” function, which reduces the maximum operating current, helps to minimize the overall chip power. Saturation detection, current sense, and overcurrent fault outputs are provided to assist the system designer. The device was fabricated on SIMOX wafers with 340 nm of Si film using our 1.25 μm CMOS SOI process with single level Ti/W interconnects and CoSi₂ contacts. Our Ti/W metallization, capped with Si₃N₄ for corrosion protection, has been evaluated to have a lifetime of ~16.7 years for 300°C operation at 10⁶ A/cm² (a 10% resistance increase was the definition of failure). The output power transistor has been formed with our standard CMOS process. Its gate dimensions were L=2 μm and W=48,000 μm, with a drain extension of 2.8 μm