Threshold voltage and transconductance shifting reliance on strained-SiGe channel dimension

• W/L ratio determines mobility change in a biaxial strained channel.
• Increased W/L ratio splits Vt and Gm of strained/unstrained p-channel.
• Dominance theory explains (2) in both n-/p-channel.
• Extreme W/L can determine interfacial stress at cap Si/SiGe.

Compared with a control Si p-channel, a compressive SiGe p-channel degrades as the width-to-length (W/L) ratio increases beyond a critical value. This ratio varies at different areas of a wafer. The threshold voltage and transconductance differences between a strained SiGe and a control Si p-channel augment as the W/L ratio increases. However, the transconductance difference in an n-channel diminishes as the ratio increases, which can be explained by the prominent longitudinal or transverse configuration of the piezoresistance coefficients of [1 1 0] SiGe. The interfacial stress between a capsulated Si and SiGe can be approximated by comparing the degradations of a strained SiGe and that of a control Si channel.