Depletion type n-MOST using lateral diffusion of P-wells in C-MOS process

A depletion type n-MOST which can be used as a stable low-level current source is realized in C-MOS technology. No additional step or modification of the process is required. The transistor is located in the region between any two closely spaced P-wells and its current path is parallel to the edges of the P-wells. Measurements on MOSTs with P-well window spacings from 8 to 14µm between two P-wells (with X
j
∼8µm) have been performed. Depending on the spacing they can be used as current sources with current values between a few nA and hundred nA at zero gate-source voltage. Flat temperature behavior of the current source can be obtained with optimum spacing. Main features of the experimental results are interpreted by means of a semi-empirical model using profile measurements and Kennedy's equations for lateral diffusion.