Elsevier

Microelectronics Reliability

Volume 91, Part 2, December 2018, Pages 194-200
Microelectronics Reliability

Impact of finger numbers on the performance of proton-radiated SiGe power HBTs at room and cryogenic temperatures

https://doi.org/10.1016/j.microrel.2018.10.006Get rights and content

Highlights

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    This work investigates the performance of proton-radiated SiGe power HBTs with different finger numbers at 300 K and 77 K.

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    The degradation mechanism was analyzed via measurement of direct current and alternating current properties.

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    Results show that the number of emitter fingers is the main affecting factor of electrical properties for radiated HBTs.

Abstract

Multi-finger silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) are attractive to the radiation-intense environment. This paper investigates the performance of proton-radiated SiGe power HBTs with different finger numbers (8, 24, 40, and 80 emitter fingers) at room and cryogenic temperatures. Different proton radiation fluences (1 × 1012 p/cm2, 2 × 1013 p/cm2, and 5 × 1013 p/cm2) and ambient temperatures (300 K and 77 K) were used to study the irradiation performance of the HBTs. Results show that the number of emitter fingers has a significant impact on the performance of the SiGe power HBTs for different temperatures and irradiation conditions. Underlying mechanisms have been discussed. This study provides guidelines on designing and using SiGe power HBTs for integrated circuits in radiation environments at room and cryogenic temperatures.

Introduction

In addition to SiGe heterojunction bipolar transistors (HBTs)' well-known advantages of compactness, light-weight, and good reliability, research shows that they are also good candidate for radiation-hard devices used in space exploration, particle physics detectors, health imaging systems, etc. [[1], [2], [3], [4], [5], [6]]. The investigation on performance of the radiated SiGe HBTs can be traced back to decades ago, for the requirement of devices used in radiation-rich environment [1]. Researchers focused on the radiation effects of single-finger SiGe HBTs and demonstrated their inherent radiation hardness in their early investigations [7,8]. Soon afterward, the damage mechanisms of single-finger SiGe HBTs under various radiation conditions have been studied. It is revealed that the emitter-base (EB) spacer (forward-mode) and the shallow trench isolation (STI) oxide (inverse-mode) of the SiGe HBTs are most sensitive to radiation damage [2,3,[9], [10], [11], [12], [13]].

In addition, compared to the low-power HBTs, high-power SiGe HBTs play an important role in the radio-frequency (RF)/microwave/terahertz (THz) communication system [6,[14], [15], [16]]. Therefore, large emitter area (AE) SiGe power HBTs are needed as core active components of power amplifiers to deliver RF power to antennas in wireless communication systems [[17], [18], [19], [20]]. However, single-finger SiGe HBTs with large-area emitter are not good options, due to the perimeter-to-area ratios' limit, which means devices with bigger perimeter-to-area ratio of emitter are more affected by radiation damage [21,22]. To solve this problem, the HBTs are optimized with multi-fingers with same emitter area, thus having a much better perimeter-to-area ratio and thermal dissipation. Performance of SiGe power HBTs has been investigated with different radiation doses and ambient temperatures [23,24]. Different from low-power single-finger devices, high-power multi-finger SiGe HBTs have more severe damages under radiation conditions, due to larger emitter area, thermal effects, parasitics, etc. However, as of today, no systematic characterization has been conducted on the performance of radiated SiGe power HBTs with different emitter finger numbers. Therefore, in this study, we have investigated the performance of proton-radiated SiGe power HBTs with different finger numbers, under various radiation doses at room and cryogenic temperatures. The SiGe HBTs suffer different performance degradations with different number of emitter fingers. The underlying mechanism is also discussed.

Section snippets

Experimental methods

Devices used in this exploration were commercial SiGe power HBTs manufactured in TowerJazz with 0.35 μm SiGe BiCMOS process [25], with more details can be found in [26]. The device discussed in this paper is multi-finger SiGe HBTs, which was fabricated by combining different number of HBT cells (2, 6, 10 and 20 cells, respectively). Each cell consists of four emitter fingers with same dimension of 0.9 × 20.3 μm2 for each finger. Fig. 1(a) shows the photograph of HBT1 with 2 cells using eight

Dc measurement results

Irradiation fluences and ambient temperatures have an effect on dc characteristics of SiGe HBTs. Therefore, the forward Gummel characteristics and current gain in pre-irradiation and post-irradiation are measured at proton radiation conditions. Fig. 2, Fig. 3 show the forward Gummel characteristics and current gain at room temperature (300 K). The forward Gummel characteristics in cryogenic temperature (77 K) are shown in Fig. 4. The noise at low current demonstrated in Fig. 2, Fig. 4 may be

The major effect of proton irradiation damage

The proton radiation damage is due to two mechanisms: the ionization damage which produces oxide trapped changes and interface states at EB spacer and the displacement damage (DD) which cause the decrease of minority carrier lifetime [9]. Although devices with small area have few displacement damage [27], the ionization damage is a major effect of proton irradiation damage [9,10,22]. Thus, in this study, we are concentrating more on the ionization damage of SiGe power HBTs.

Dose and temperatures' effects on proton radiated devices

For a given device,

Conclusion

In this study, we investigate the performance of proton-radiated SiGe power HBTs with different finger numbers (8, 24, 40, and 80 emitter fingers) at room and cryogenic temperatures. Different proton radiation fluences (1 × 1012 p/cm2, 2 × 1013 p/cm2, and 5 × 1013 p/cm2) and ambient temperatures (300 K and 77 K) were used to study the irradiation performance of HBTs. The influences of emitter finger numbers and proton radiation on the performance of SiGe power HBTs at different temperatures

Acknowledgments

This work was supported by the National Natural Science Foundation of China (grant number 61871285) and Tianjin Natural Science Foundation (grant number 18JCYBJC15900).

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