Si/SiGe field-effect transistors*

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Abstract
Over the last few years, SiGe heterodevices with outstanding rf performance have been introduced to meet the needs of modern consumer electronics, which require novel silicon-based low cost–high speed components with improved current gain, low noise, and reduced power consumption operating in the GHz range. This article reviews device and the first circuit results of lateral modulation doped SiGe modulation doped hetero-field-effect transistors (MODFETs) with Schottky gates as well as lateral and vertical SiGe metalorganic field effect transistors (MOSFETs) focusing on dc characteristics, rf performance comprising cutoff frequencies, delays, and on layer design. With an fmax, of up to 92 GHz, the highest maximum frequency of oscillation reported so far for any Si-based FET, and transconductances gme up to 470 mS/mm, the n-SiGe MODFET is presently improving in speed with combining the advantages of heterodevices with well-established Si technology. For p-SiGe MODFETs cutoff frequencies ft of 70 GHz and fmax of 84 GHz have been measured. A reduced gate leakage and an improved voltage swing is achieved using MOS-gated heterodevices. For p-channel SiGe hetero-MOSFETs room temperature transconductances up to 210 mS/mm for 0.25 μm gate-length devices have been measured. Vertical MOSFETs allow further device scaling into the deep sub-100 nm range and thus enable us to overcome performance limits due to minimum feature sizes using state-of-the-art lithography techniques.