Consider a MOSFET biased such that carriers are traveling at...

Consider a MOSFET biased such that carriers are traveling at their saturated velocity in the $\mathrm{n}$ channel. If constant-field scaling is applied to the device, how does the drain current scale?

Key Concepts

Scaling of Drain Current under Constant-Field Scaling

When constant-field scaling is applied to a velocity-saturated MOSFET, while the induced charge per unit area remains effectively constant (since voltage and oxide capacitance scale inversely), the physical width of the transistor, which directly influences the total current, scales by the same factor as the other dimensions. Consequently, the drain current scales inversely with the scaling factor, meaning that as the device dimensions shrink, the drain current decreases proportionally.

Drain Current in a Velocity-Saturated MOSFET

In a MOSFET operating in the velocity-saturation regime, the drain current is dominated by the carrier’s saturated velocity and the inversion charge in the channel. Unlike the quadratic dependence seen in long-channel devices, here the current is approximately given by the product of the channel width, the charge per unit area, and the saturated velocity, making the current less sensitive to channel length reductions.

Constant-Field Scaling

Constant-field scaling is a technique used in transistor design where all dimensions of a device—including channel length, channel width, and oxide thickness—are scaled by the same factor while simultaneously scaling the voltages. This preserves the electric fields within the device, ensuring that the device does not experience excessive field strengths during downscaling.

Velocity Saturation

Velocity saturation refers to the phenomenon where carriers in a semiconductor channel reach a maximum drift velocity despite increases in the electric field. This is particularly important in short-channel devices where high electric fields cause the carrier velocity to saturate at a constant value, typically determined by material properties.

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