The thermal characteristics of SOI SiGe HBT with SiO2/Si3N4/SiO2 insulators

In order to improve the thermal characteristics of SOI SiGe HBT, a novel structure of SiO
₂
/Si
₃
N
₄
/SiO
₂
insulators is proposed, considered that the thermal conductivity of Si
₃
N
₄
is much higher than that of SiO
₂
. With the aid of the thermal-electrical model of SOI SiGe HBT with SiO
₂
/Si
₃
N
₄
/SiO
₂
insulators, the thermal characteristics of the device is studied. The thermal resistance (R
_th
), thermal time constant (τ), and thermal capacity (C
_th
) are adopt to represent the steady-state and transient thermal characteristics, respectively. It is shown that R
_th
, τ, and C
_th
of the novel device are decreased by 19.6%, 24.14%, and 5.36%, respectively, when compared with that of traditional SOI SiGe HBT with SiO
₂
insulator. In addition, for the novel device, the improvement of R
_th
and τ is kept with the increase of the dissipated power from 2mW to 12mW. Furthermore, for the novel device, the influence of Si
₃
N
₄
thickness on R
_th
and τ is also studied. All of R
_th
, τ, and C
_th
are decreased with the increase of the thickness of the Si
₃
N
₄
(t
_Si3N4
). Both the trend of R
_th
and τ can be approximated by a linear function with t
_Si3N4
, while the trend of C
_th
can be approximated by an exponential function. The results above provides a guideline to the improvement of the thermal characteristics of conventional SOI SiGe HBTs, making the device more suitable for high-temperature applications.