Gaoqing Li

The total-dose-effects of gamma and proton irradiations on high-voltage silicon–germanium heterojunction bipolar transistors

The total-dose-effects of gamma and proton irradiations on high-voltage silicon–germanium heterojunction bipolar transistors with the collector electrode elicited from the backside of the substrate are investigated. Pre- and post-radiation DC characteristics of the transistors are used to quantify the dose tolerance to the two different irradiation sources. Measurement results indicate that the devices exhibit a total dose tolerance up to Mrad level. The device response is indeed radiation source dependent and the proton irradiation can produce a more significant damage than the gamma irradiation, causing more pronounced performance degradation. The experimental results from both irradiations are compared and discussed in detail, and furthermore the underlying physical mechanisms are analyzed and investigated. The considerably different degradation behaviors are attributed to the extra displacement damage besides ionizing damage induced by the proton irradiation.

Novel extraction of emitter resistance of SiGe HBTs from forward-Gummel measurements

A simple dc method for determining the emitter series resistances of bipolar transistors from the measured forward-Gummel characteristics is proposed. The method is successfully applied to a set of SiGe HBTs with different sizes, which have been fabricated and measured over a large temperature range. As a result, the temperature scaling and geometric scaling characteristics of the extracted emitter series resistances are analyzed and discussed.

A Darlington SiGe microwave monolithic integrated circuit

This paper presents a low noise Darlington SiGe microwave monolithic integrated circuit (MMIC). The circuit consisting of two SiGe hetero-junction bipolar transistors and four resistors is convenient to cascade without any other matching circuit. It is fabricated in a quasi-self-aligned process, with a nonselectively grown epitaxial SiGe base. The small resistor R4 is critical to smooth the gain band, lower the input and output voltage-static-wave ratio (VSWR) in a broad band, so it is made differently from the other three. The measurement results give the cutoff frequencies of SiGe HBTs 10.9 GHz and 9.2 GHz respectively. At 1 GHz, the noise figure of the circuit is 1.59 dB, the power gain is 16.1 dB, the input and output VSWR is 1.6 and 2.0

An accurate parameter extraction method for RF LDMOSFET small-signal model

A new direct parameter extraction method of small-signal equivalent circuit for radio frequency laterally-diffused Metal Oxide Semiconductor Field Effect Transistor (RF LDMOSFET) with Faraday shield biased in cut-off operation is presented in this paper. A series of analytical equations are derived for non-linear rational function fitting as well as linear regression to measured device frequency response characteristics. The method is successfully applied to a set of fabricated RF LDMOSFETs with different geometry scales. As a result, all of the cut-off small-signal equivalent circuit elements are determined. Validation of the extraction method is verified by good agreement between the simulation results and the corresponding measurement data. In addition, reasonable physical meaningfulness of the method is further demonstrated by characterizing the device geometrical dependences of the extracted gate-drain capacitance (Cgd) and drain-source capacitance (Cds).

The reliability of SiGe HBT under swift heavy ion irradiation

Silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) were irradiated by 25Mev Si4+ ion with equivalent absorbed dose from 300 krad(Si) to 10 Mrad(Si). Pre- and post-irradiation direct current (DC) characteristics were used to quantify the dose tolerance to the heavy ion irradiation. Base current was found more sensitive than collector current and current gain appeared to decline with the ion fluence increasing. An unexpected increase in emitter current was observed in the reversed-mode operation. The reverse leakage current of base-collector and base-emitter junction increased with the increase in ion fluence. The displacement damages were thought to be mainly contributed to performance degradation of SiGe HBT.

Cascadable direct-coupled wideband SiGe HBT MMIC [amplifier]

This paper reports the design and performance of a single-stage Darlington-structure SiGe hetero-junction bipolar transistor (HBT) microwave monolithic integrated circuit based on an advanced SiGe HBT technology. The circuit has 11.6 dB gain at 850 MHz and 8.0 dB gain at 1950 MHz. The input and output VSWRs are 3.01:1 and 2.66:1 at 3000 MHz, respectively. This circuit consumes 140 mW DC power and has a chip size of 0.32/spl times/0.42 mm/sup 2/.