Layout-Dependent Stress Effect on High-Frequency Characteristics and Flicker Noise in Multifinger and Donut MOSFETs

The impact of MOSFET layout-dependent stress on high-frequency performance and flicker noise has been investigated. The proposed donut MOSFETs demonstrate the advantages over the standard multifinger MOSFETs, such as the lower flicker noise $S_{\rm ID}/I_{\rm DS}^{2}$ in the low-frequency domain and the higher cutoff frequency $f_{T}$ in the very high-frequency region. The elimination of the transverse stress $ \sigma_{\perp}$ from shallow trench isolation (STI) and the suppression of interface traps along the STI edge are proposed as the primary factors responsible for the enhancement of the effective mobility $\mu_{\rm eff}$, as well as $f_{T}$, and the reduction of flicker noise. The significantly lower flicker noise realized by donut devices suggests the reduction of STI-generated traps and the suppression of mobility fluctuation due to eliminated transverse stress. The former is applied to n-channel MOS in which the flicker noise is determined by the number-fluctuation model. The latter is responsible for p-channel MOS whose flicker noise is dominated by the mobility-fluctuation model.