Isothermal DC and microwave characterizations of power RF silicon LDMOSFETs

Presented in this paper are two new approaches for the acquisition of both isothermal DC current-voltage (I-V) characteristics and microwave S-parameters of power RF LDMOSFETs. In the first approach, a 3D tensor product B-spline representation is used to extract isothermal DC I-V characteristics from DC I-V characteristics measured at various substrate temperatures. The average device surface temperature is measured using an infrared sensor. A single effective thermal resistance is found to map the entire electrothermal profile of the device, justifying the isothermal DC I-V definition used. In the second approach, isothermal I-V and microwave data are directly measured with an efficient procedure that keeps the average device surface temperature constant. Excellent agreement is obtained between the numerical extraction and the direct measurement approach. Finally, the comparison of the transconductance extracted from the isothermal DC I-V and microwave data confirms the presence of a small low-frequency dispersion in LDMOSFETs not due to self-heating.