The wafer micrograph in Fig. 5.20 shows the fabricated lateral IGBT and the integrated sensor contact positions. The dc performance was tested with various anode bias, gate bias, and device temperature. A special heating platform was set up to maintain the wafer at a predefined elevated temperature. Measurements were made for the linear region (function as a power switch) as well as the saturation region (function as an amplifier).
Fig. 5.19. Device profile obtained by process simulation.
Fig. 5.20. The micrography of a fabricated lateral IGBT with integrated current sensor.
Fig. 5.21. Variations of current sensing ratio against anode current at various temperatures (under linear operating mode, as a switch) with a constant gate bias.
DC Measurement in the Linear Operating Region (Switch Operation)
Figure 5.21 shows the measured values of sensing ratio over a range of temperatures with anode current values between 250 mA and 600 mA per cell group. The curves show that the sensor current ratio remains fairly constant with the anode current density and has a stronger dependence on the temperature variations. It is observed that the sensing ratio becomes less dependent on temperature variation at a higher temperature. A total variation of around ±5.2% from the average sensing ratio is observed when the device is at temperature range between 303 K and 403 K.
The gate bias sensitivity on the current sensing ratio is shown in Fig. 5.22. The values of sensor ratio change in a peak-to-peak range from 1.96% to 2.41% (or within ±1.21%) with the gate voltage. The sensing ratio changes by ±5.22% for temperature from 303 K to 403 K as seen. A similar characteristic is observed that the temperature variation dominates the current ratio variation and the effect becomes weaker toward the higher temperature region.