Patent ID: 8441833

Claim:
A method of screening non-volatile latch circuits, each latch circuit comprising cross-coupled inverters driving first and second storage nodes, a first ferroelectric capacitor having a first plate coupled to the first storage node, and a second ferroelectric capacitor having a first plate coupled to the second storage node, the method comprising: characterizing each of a plurality of latch circuits by performing a plurality of operations comprising: setting the state of the latch circuit so that the first and second storage nodes are at low and high logic states, respectively; then polarizing the first and second ferroelectric capacitors to opposite polarization states, corresponding to the state of the latch circuit, by applying low and high bias voltages to a second plate of the first ferroelectric capacitor and a second plate of the second ferroelectric capacitor; then removing bias from the cross-coupled inverters of the latch circuit; then biasing the second plate of the first ferroelectric capacitor to a first bias voltage, and biasing the second plate of the second ferroelectric capacitor to a second bias voltage, the second bias voltage lower than the first bias voltage by a differential voltage; then applying bias to the cross-coupled inverters of the latch circuit; then reading the state of the latch circuit; adjusting the differential voltage; and repeating the setting, polarizing, removing, biasing, applying, reading, and adjusting operations to determine a fail differential voltage that causes the reading operation to sense a state of the latch circuit opposite from that set in the setting step; stressing the plurality of latch circuits; evaluating the stressed plurality of latch circuits; and then determining a screen differential voltage from the evaluated plurality of latch circuits.