On the Cryogenic RF Linearity of SiGe HBTs in a Fourth-Generation 90-nm SiGe BiCMOS Technology

PROJECT TITLE :

On the Cryogenic RF Linearity of SiGe HBTs in a Fourth-Generation 90-nm SiGe BiCMOS Technology

ABSTRACT:

Large-signal ( $P_rm 1,dB$ ) and small-signal (OIP3) radio frequency (RF) linearities of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) fabricated during a new fourth-generation 90-nm SiGe BiCMOS technology operating at cryogenic temperatures are investigated. The SiGe BiCMOS process technology has an $f_T$ / $f_rm max$ of 300/350 GHz. SiGe HBTs with two different layout configurations, collector-base-emitter (CBE) and CBE-base-collector (CBEBC), were characterised over temperature. Each dc and ac figures-of-advantage are presented to aid in understanding the linearity, and to supply an overall performance comparison between the two layout configurations. The extracted peak $f_T$ / $f_rm max$ for CBE and CBEBC at seventy eight K are 387/350 and 420/410 GHz, respectively. The $P_rm 1,dB$ and OIP3 linearity metrics for each configurations are comparable. Source- and load-pull measurements were performed at each temperature at 8 and eighteen GHz, with the devices biased at a $J_C$ of eighteen mA/ $mu textm^2$ . Two-tone measurements over bias were additionally performed at three hundred and 78 K with fifty- $Omega $ terminations for the supply and load impedances. The 50 $Omega $ results follow an analogous response to the source- and load-pull measurements at three hundred an- 78 K, and demonstrate that the tiny-signal linearity of the SiGe HBTs is not adversely impacted by operation at cryogenic temperatures. The CBEBC configuration demonstrated the most consistent RF linearity performance at cryogenic temperature out of the two layout choices.

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