Time-Domain Characterization of Lattice Heating in Power VDMOSFETs by Means of an Interferometric Laserprobe Technique

An experimental method for the absolute measurement of the transient lattice temperature increase in power VDMOSFETs is proposed. The technique detects changes in the refractive index of silicon due to heating in dynamic device operation, which modulate the phase of an infrared laser beam focused on the device from the substrate side. The experiments are supported by numerical modeling of the heat conduction within the VDMOSFET-chip combined with modeling of the laser beam modulation. The simulation results are verified by electrical characterization and are used to calibrate the optical system via the temperature coefficient of the refractive index in silicon, which is found to be dn/dT = 1.57* 10
^-4
K
^-1
.