J. Tasselli

Electrical behavior of double heterojunction NpNGaAlAs/GaAs/GaAlAs bipolr transistors

Abstract This paper deals with a theoretical and experimental study of double heterojunction NpN GaAlAs/GaAs/GaAlAs bipolar transistors fabricated by liquid phase epitaxy. Starting from the general transport equations of the macroscopic theory of diffusion, a charge-control-type model is first established. The compact analytical expressions which determine the transfer characteristics (JC′VBE) and intrinsic current gain h FE ∗ are expressed as a function of the technological or geometrical parameters of the structure. A study of the sensitivity to these parameters highlights in particular the influence of the zone including the conduction band spike of the base collector heterojunction. Such an influence may assume the form of a substantial degradation of the devices electrical characteristics (reduction of the base transfer factor, increase in transit time). The experimental behavior observed on characterized devices confirms the theoretical predictions.

Transistor‐based evaluation of conduction‐band offset in GaInP/GaAs heterojunction

The conduction‐band discontinuity for GaInP/GaAs metalorganic chemical vapor deposition (MOCVD) HBTs has been determined from current–voltage characterization. The charge‐control model used permits to compare the respective weights of collector current limitations due to the potential barrier effect and to the carrier diffusion mechanism in the low gap base region. A study of sensitivity to the main sources of error leads to a conduction‐band offset value of ΔEC≊170±16 meV confirming the advantage of the resulting band lineup for the HBT.

Theory and experiment of the temperature dependence of GaAlAs/GaAs HBTs characteristics for power amplifier applications

Abstract Modelling of thermal effects of GaAlAs/GaAs HBTs d.c. and r.f. characteristics is presented. The thermal resistance value is determined experimentally and introduced in a model. Good agreement between measured results and those from modelling is demonstrated. The r.f. performance shows a good stability at high temperature (fmax is reduced by about 12% due to temperature rise). For the high signal mode, the simulation of a power amplifier at 3 GHz is also carried out with and without temperature effects.

New polysilicon sensor and actuator technology for the development of a thermal platform

This paper reports on a generic approach for the development of polysilicon diodes on glass wafers for thermal sensing and control applications. The capabilities of polysilicon diodes as thermal sensors are demonstrated on glass wafers with good thermal sensitivities about 40mV/ºC. A simple experimental set-up has been developed to evaluate the potentialities of these devices in microfluidics operating conditions. First encouraging results of temperature detection are presented.

Electrical qualification of new ultrathin integration techniques

Abstract The aim of this paper is to analyze the feasibility of ultrathin packages through the electrical qualification of the technological process used, i.e. mechanical lapping. It considers polysilicon bipolar transistors which thickness can reach values lower than 10 μm. Forward mode and reverse mode characterizations show no significant degradation of pertinent characteristics, thus allowing to find applications in new compact packaging concept.

Influence of the topology on thermal dissipation in high power density GaAs devices

Abstract This paper presents an analysis of the influence of the active zone topology on the heat dissipation for GaAs devices. It highlights the influence of the width and the form factor on the thermal behavior of the device. It also shows the sensitivity of the thermal resistance to the increase of the dissipated power. For multi-cellular structures the impact of the thermal coupling between heat sources is studied.

Emitter excess resistance in GaAlAs/GaAs heterojunction bipolar transistors

Numerous studies have shown the influence of parasitic elements, particularly emitter access resistance and inductance, on HBTs DC and dynamic performances. Instead the achievement of low specific contact resistances, the apparent emitter resistance presents high values. To explain this discrepancy the longitudinal distribution of the emitter current has been investigated by using a distributed DC-model, taking into account the metal layers resistance of the different contacts. Thus it is shown that only the emitter contact parameters act on the non equipotentiality along the structure.