Excellent High Frequency Performance Research Articles

High speed SiGe heterobipolar transistors

SiGe heterobipolar transistors are near the point of commercial availability. They will be inserted in mobile phones in the 0.9 to 2.4 GHz range and in wireless local area networks using the 2.4 to 5.8 GHz band. The advantage of SiGe HBTs is not only their excellent high frequency and noise performance with a maximum frequency of oscillation up to 120 GHz and 0.9 dB noise figure at 10 GHz, but the compatibility of SiGe to standard silicon technology. Fabrication processes and results of a research-like SiGe HBT and a possible production type HBT version are described. In addition, some circuit demonstrators for SiGe ICs will be presented.

InAlAs/InGaAs high electron mobility transistors on low temperature InAlAs buffer layers by metalorganic chemical vapor deposition

InAlAs/InGaAs high electron mobility transistors (HEMT) with excellent high frequency performance were demonstrated. Device sizes of 0.25×50 μm and 0.10×50 μm showed current gain cutoff frequencies of 143 and 205 GHz, respectively. The HEMT structures were grown on a low temperature InAlAs buffer layers designed to eliminate conductive impurity spikes situated at the epitaxial/substrate interface. The highly resistive buffer layer (2×105 Ω cm) was obtained at a growth temperature of 475 °C using a combination of trimethylarsenic and arsine as the arsenic sources.

The application of polypyrrole as counterelectrode in electrolytic capacitors

Solid electrolyte capacitors in which the counterelectrode MnO 2 is replaced by polypyrrole have been prepared and investigated. The dopant counterions of the polypyrrole electrode were varied and the influence on capacitor performance related to differences in material properties. This was verified both for zero-hour characteristics as for lifetime experiments at 125 °C in air. Capacitors with napthatlenesulfonate as counterion were very stable and showed an excellent high frequency performance, comparable with a ceramic multilayer capacitor.

New CMOS NIC-based MOSFET-C filters

A new CMOS NIC-based MOSFET-C integrator and its filter applications are presented. Based on this integrator, the required filter chip area and manufacturing cost can be reduced. A third-order elliptic lowpass ladder filter with 0.02dB ripple and bandwidth up to 1.0MHz is designed and simulated. The excellent high frequency performances of these NICs will facilitate the realisation of high frequency integrated filters.

Very high frequency performance of nanometre scale GaAs MESFETs

GaAs MESFETs with gate lengths from 300 nm down to 40 nm have been fabricated and characterised at microwave frequencies. The MESFETs have excellent DC and high frequency performance. It is shown that the unity gain cut-off frequency f/sub T/, is not inversely proportional to the gate-length, as a consequence of carrier transit delays.