Methods and systems of cell-array programming for neural compute using flash arrays

A method for NOR flash cell-array programming in a neural circuit comprising:

• erasing a cell array;
• programming a set of reference cells of a reference cell array to a target reference threshold voltage (Vt_ref);
• generating, with the reference cells, a current or voltage, reference signal;
• using the reference signal to bias a neural cells during verification of program state of the neural cells to achieve their respective target threshold voltages (Vt_cell);
• and
• programming a set of neural cells of a neural cell array to their respective target threshold voltages, wherein a neural cell comprises a flash-cell system, wherein an equation for a neural cell comprises Eqneuron≡Σ(xi*yi)+b, where, xi is the set of input vectors, yi is parameter which is related to a threshold voltage of individual flash cells, and b is a bias variable,
• wherein the cells are first programmed to a pre-final threshold values (Vt_initial_1) as defined in yi in a first sequence on program and program verify pulses as defined in xi,
• wherein the cells are then programmed to a second pre-final threshold values (Vt_initial_2) as defined in yi in a second subsequent sequence of program and program verify pulses as defined in xi, and where the second pre-final threshold values are larger than the final target threshold values, and
• wherein the cells are then weak erased to the final target threshold values as defined in yi with a sequence of erase pulses and erase verify pulses,
• wherein the final threshold value is considered reached if the threshold value is close to (less than or equal to) the final target threshold value,
• wherein the weak erase comprises an erase voltage level only detraps a plurality of shallow traps in an oxide layer or a nitride layer of the flash cell without effectively changing the threshold voltage.