The impact of self-heating and SiGe strain-relaxed buffer thickness on the analog performance of strained Si nMOSFETs

• Published in: Solid-state electronics 2010-03, Vol.54 (3), p.327-335
• Main Authors: Alatise, O.M., Kwa, K.S.K., Olsen, S.H., O’Neill, A.G.
• Format: Article
• Language: English
• Subjects: Analog MOSFET; Applied sciences; Buffers; Devices; Drains; Electric potential; Electronics; Exact sciences and technology; Self-gain; Self-heating; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Silicon; Silicon germanides; Silicon–germanium; Strained silicon; Transistors; Voltage
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2009.09.029

The impact of the thickness of the silicon–germanium strain-relaxed buffer (SiGe SRB) on the analog performance of strained Si nMOSFETs is investigated. The negative drain conductance caused by self-heating at high power levels leads to negative self-gain which can cause anomalous circuit behavior like non-linear phase shifts. Using AC and DC measurements, it is shown that reducing the SRB thickness improves the analog design space and performance by minimizing self-heating. The range of terminal voltages that leverage positive self-gain in 0.1 μm strained Si MOSFETs fabricated on 425 nm SiGe SRBs is increased by over 100% compared with strained Si devices fabricated on conventional SiGe SRBs 4 μm thick. Strained Si nMOSFETs fabricated on thin SiGe SRBs also show 45% improvement in the self-gain compared with the Si control as well as 25% enhancement in the on-state performance compared with the strained Si nMOSFETs on the 4 μm SiGe SRB. The extracted thermal resistance is 50% lower in the strained Si device on the thin SiGe SRB corresponding to a 30% reduction in the temperature rise compared with the device fabricated on the 4 μm SiGe SRB. Comparisons between the maximum drain voltages for positive self-gain in the strained Si devices and the ITRS projections of supply-voltage scaling show that reducing the thickness of the SiGe SRB would be necessary for future technology nodes.