Modelling of Silicon Germanium Heterojunction Bipolar Transistors and its Applications

Staffan Bruce

Licentiate Thesis, Report UPTEC 97126R, November 1997.

Abstract:

This thesis concerns modelling of Si/Si1-xGex Heterojunction Bipolar Transistors (HBT) and its applications. A physics-based large signal model including thermal dependence has been developed for Si/Si1-xGex HBTs. The alloying composition for the modelled device may vary between 0£ x£0.30, having a pure silicon transistor as a special case.

The model takes into account several effects that are important for the operation of Si/Si1-xGex HBTs and is directly related to the parameters in the fabrication process. Using extraction procedures for only a few parameters that inherently are difficult to predict, either due to uncertainties in the fabrication process or due to complex physical relations, a good agreement is found between the model and measurements.

A new technique for extracting the thermal time constant of a device using small signal measurements is presented. The fitting procedure of electrical model parameters against measured data is described in the DC-case and particular effects are discussed. In the RF-case, effects from the variation of key equivalent circuit parameters on the different scattering parameters are discussed.

With the model, a frequency doubler has been designed and fabricated. Measured results showed a conversion, from input frequency of 27.5 GHz to output frequency of 55 GHz, of -14 dB. Better results can be anticipated since the HBT in the fabricated circuit differed from the one used in the design. The agreement between simulated and measured data were good.

Keywords:

SiGe, HBT, Large-signal modelling, thermal time constant, frequency doubler.

Related publications:

Extraction of thermal time constant in HBTs using small signal measurements.Electronics Letters 1997.
In Postscript : compressed(gz) 64K , uncompressed 334K.

On the design of a 55 GHz Si/SiGe HBT frequency doubler operating close to fmax. Proc. 26th European Microwave Conference, Prague 1996.
In Postscript : compressed(gz)584K , uncompressed1.56M.

Development, implementation and verification of a physics-based Si/SiGe HBT model for millimeter-wave non-linear circuit simulations. Proc. 26th European Microwave Conference, Prague 1996.
In Postscript : compressed(gz)30K , uncompressed131K.

Source:

Introduction in Postscript, 58K ; in Pdf, 18K