Natural length (scale length, λ): definition

Beginner

How far the drain’s influence reaches into the channel. The gate stays in charge only if the channel is several times longer than this.

Novice

A length set by the shape and materials of a transistor that says how far the electric field of the source and drain spreads under the gate. A device behaves well when its gate is several natural lengths long.

Expert

The decay length of the 2D Poisson solution along the channel, $\lambda \approx \sqrt{\varepsilon_{\mathrm{Si}}\, t_{\mathrm{ch}}\, t_{\mathrm{ox}} / (N \varepsilon_{\mathrm{ox}})}$ in the simple model, where $N$ grows with the number of gated sides. Short-channel effects scale as $\exp(-L/2\lambda)$ , so minimum $L$ is a multiple of $\lambda$ (about $3\lambda$ for planar bulk in published scaling theory).