Ningyue Jiang

An 18-GHz 300-mW SiGe power HBT

An 18-GHz, 300-mW SiGe power heterojunction bipolar transistor (HBT) is demonstrated. The optimization of SiGe HBT vertical profile has enabled this type of devices to operate with high gain and high power at this high frequency. In the common-base configuration, a continuous wave output power of 24.73 dBm with a power gain of 4.5 dB was measured from a single 20-emitter stripe SiGe (2/spl times/30 /spl mu/m/sup 2/ of each emitter finger) double HBT. The overall performance characteristics represent the state-of-the-art SiGe power HBTs operating in the K-band frequency range.

Base region optimization of SiGe HBTs for high-frequency microwave power amplification

The base region optimization of SiGe power HBTs for high frequency power amplification is investigated. Employing a heavily doped base in conjunction with a high Ge content can effectively improve the large-signal power gain values of SiGe HBTs while maintaining their high breakdown voltages and thus allow them to be efficiently operated with high power at higher frequencies. With such a base region optimization, not only lateral scaling requirement can be relaxed, but also common-base configuration for power amplification using these devices can be favored, which further enhances power gain values of SiGe power HBTs at high frequencies. Load-pull experimental results are presented to show the highest figure of merit power performance of SiGe power HBTs with an optimized base region. Power performance at X-band with different base region designs was also compared to illustrate the significant benefits that are resulted from base optimization.

Boosting up performance of power SiGe HBTs using advanced layout concept

We report an advanced power device layout structure, namely heat transfer counterbalanced (HTCB) layout, for designing power SiGe HBTs. It is shown that this new power device structure can substantially reduce adverse thermal effects of power devices without using ballasting resistors. Significantly improved power performances have been achieved from SiGe power HBTs employing the new layout concept.

Cryogenic operation of a 24 GHz MMIC SiGe HBT medium power amplifier

The performance of a SiGe heterojunction bipolar transistor (HBT) millimetre-wave power amplifier (PA) operating at cryogenic temperature was reported and analysed for the first time. A 24 GHz two-stage medium PA employing common-emitter and common-base SiGe power HBTs in the first and the second stage, respectively, showed a significant power gain increase at 77 K in comparison with that measured at room temperature. Detailed analyses indicate that cryogenic operation of SiGe HBT-based PAs mainly affects (improves) the performance of the SiGe HBTs in the circuits due to transconductance enhancement through magnified, favourable changes of SiGe bandgap due to cooling (ΔEg/kT) and minimized thermal effects, with little influence on the passive components of the circuits.

Fundamental Difference of Power Handling Between CE and CB HBTs

Fundamental power handling of common-emitter (CE) and common-base (CB) (SiGe) power HBTs is compared by measuring their dynamic load lines under large-signal operation with input and output matched for maximum output power (Pout). The distinct difference of load lines indicates the fundamental different power amplification mechanisms between the two configurations. It is shown that under voltage-source bias the CE configuration always provides higher (saturated) output power (Pout) than the CB configuration, while higher power gain and power added efficiency (PAE) could be obtained from the CB configuration than the CE configuration before entering the power saturation region

Impact of Proton Radiation on the Large-Signal Power Performance of SiGe Power HBTs

The effects of proton irradiation on the RF power performance of SiGe power HBTs are, for the first time, reported in this work. Large emitter area high-power SiGe HBTs fabricated in a commercial BiCMOS process were irradiated with proton, at fluences up to 2times1013 p/cm2. Besides DC and small-signal AC characterizations, on-wafer large-signal high-power performance was characterized by load-pull measurements for pre- and post-radiation devices. It is shown that, in addition to DC and small-signal AC performance, the power performance of SiGe power HBTs also exhibits excellent tolerance to high-fluence proton radiations. Only a minor degradation (from the worst measurement case, 0.7 dB degradation in power gain, 8% degradation in PAE) was measured for post-radiation devices under class-AB bias at 1.9 GHz. Moreover, the source and load impedance matching points tuned for the optimum power performance of the devices, which are critical in the design of power amplifiers, are also shown to be robust to proton radiation. This work demonstrates the potential of SiGe power HBTs in the applications of power amplifiers for wireless application under severe radiation environment even without any intentional radiation hardening

Configuration Dependence of SiGe HBT Linearity Characteristics

Linearity characteristics between common-emitter (CE) and common-base (CB) SiGe HBTs are compared at different frequencies, under different bias conditions and at different input/output matching conditions in this paper. It is shown that, without impedance matching at input/output of the devices, the CB configuration exhibits better linearity than the CE configuration under the same input power level and the difference of IMD3 between the two configurations decreases with the increase of operation frequency. However, when both input and output of the devices are impedance-matched for maximum output power Pout , the CE configuration has better linearity than the CB configuration. Furthermore, without varying the input/output matching, the linearity of the two configurations varies with bias in different ways that the linearity of the CE configuration degrades and that of the CB configuration improves as the bias is increased. Under certain impedance and bias conditions, the CB configuration can provide better linearity, besides higher power gain, than the CE configuration

SiGe power HBT design considerations for IEEE 802.11 applications

SiGe power HBTs integrated in SiGe BiCMOS are developed and characterized at 2.4 GHz for 802.11b and 5.8 GHz for 802.11a wireless LAN applications. Design considerations of ballast resistors for SiGe power HBTs at these two frequencies are investigated for both good thermal stability and high RF power performance. The investigations show that emitter ballast resistors or base ballast resistors should be judiciously used for SiGe power HBTs operating at different frequencies in order to extract the best RF performance from these devices. An RF output power of 30.8 dBm with PAE of 50.2 % at 2.4 GHz and an output power of 27.3 dBm with PAE of 23.6 % at 5.8 GHz are achieved from single discrete SiGe power HBTs with 0.4 /spl mu/m emitter width, respectively. These highest performance results demonstrate the great power amplification potential of SiGe HBTs for 802.11 wireless LAN applications.

Dc characteristics of proton radiated SiGe power HBTs at cryogenic temperature

The dc performances of proton irradiated silicon-germanium (SiGe) power heterojunction bipolar transistors (HBTs) at cryogenic temperature are reported in this work. Large emitter area high-power SiGe HBTs fabricated in a commercial BiCMOS process were irradiated with proton, at different fluences from 1×1012 p/cm2 to 5×1013 p/cm2. We show that proton radiated SiGe power HBTs are naturally suitable for electronic operations at cryogenic temperature. Specifically, investigation of proton radiation on SiGe power HBTs at liquid nitrogen temperature (77K) indicates a significant potential for space applications. The results demonstrate the potential of SiGe power HBTs in power amplification for wireless applications under severe radiation and extreme temperature environment (cryogenic) even without any intentional radiation hardening.

Effects of proton irradiation on SiGe HBTs implemented with isolation guard rings

The effects of proton irradiation on SiGe HBTs implemented with isolation guard rings are investigated in this work. Different from what was shown in any of the previous radiation tolerance studies, a distinctive increase of the emitter current after proton irradiation was observed on a measured inverse-mode Gummel plot from the SiGe HBTs implemented with isolation guard rings. Detailed device measurements and modeling revealed a new SiGe HBT degradation mechanism under proton irradiation. It is found that the increase of the emitter current measured in the inverse-mode Gummel plot comes from the degradation of the substrate–collector (buried layer) junction diode associated with the SiGe HBTs. Furthermore, we identified that the radiation damages in the substrate–collector junction near the deep trench edges are solely responsible for the observed degradation of radiation tolerance. The potential impact of this radiation damage to device operation is discussed.