A physical thermal resistance model for vertical BJTs on SOI

Because BJT currents are highly temperature sensitive, self-heating is very important in analog BJT circuits. Dielectrically isolated BJTs (DIBJTs) typically have thermal resistance R/sub TH/ three or more times higher than their bulk counterparts. Circuit simulators are readily modified to account for such effects, but characterizing thermal effects in DIBJTs is rather difficult: self-heating complicates extraction of the temperature dependences and R/sub TH/, and models that predict R/sub TH/ in bulk BJTs do not apply for SOI because of the more complicated boundary conditions. This paper describes a scalable model for R/sub TH/ in vertical DIBJTs, along with a technique for extracting R/sub TH/ in BJTs. The modeled measurements are shown to agree quite well.