Geometry effect on SiGe heterounction bipolar transistor unit cell for 1W high-efficiency RF power amplifier applications

Hwann Kaeo Chiou, Ping Chun Yeh, Chwan Ying Lee, John Yeh, Denny Tang, John Chern

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The effect of geometry on the RF power performance of silicon-germanium heterojunction bipolar transistor (SiGe HBT) unit cells is investigated using various emitter finger spacing (5). Two unit cells, namely, HBT-I and HBT-2 with the same emitter area of 8 × 0.6 × 10 μm3 but with different S values are thoroughly discussed. The S values of HBT-I and an HBT-2 are 2 and 5 μm, respectively. The obtained measurements, including DC characteristics and small- and large-signal performance characteristics of high-breakdown SiGe HBT unit cells, are presented. The HBT-1 in class-AB operations at 2.4GHz achieves an output 1 dB compression point (OP 1dB) of 16.0dBm, a maximum output power of 17.4dBm, and a peak-power added efficiency (PAE) of 59.1%. Under the same testing conditions, HBT-2 achieves an OP1dB of 19.6 dBm, a maximum output power of 20.6 dBm, and a PAE of 64.5%. HBT-2 yields significant improvements in all power performance parameters compared with HBT-1, such as 3.6dB in an OP 1dB, a maximum output power of 3.2dB, a PAE of 5.4%, and an improvement in the power performance figure of merit (FOM) of approximately 50%, which is attributed to the fact that HBT-2 has a lower thermal effect than HBT-1. The thermal effect affects both DC and output power characteristics. A 1W power device fabricated by combining eight HBT-2 unit cells achieves a power gain of 14.5 dB and a maximum PAE (PAEmax) of 75% in a class-AB operation at 2.4GHz. The power density is calculated to be up to 2.6mW/μm2. These results demonstrate that SiGe HBT technology has great potential for high-power amplifier applications.

Original languageEnglish
Pages (from-to)917-925
Number of pages9
JournalJapanese Journal of Applied Physics
Issue number3 A
StatePublished - 8 Mar 2007


  • Power amplifier
  • Power device
  • Power unit cell
  • Self-heating effect
  • SiGe HBTs


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