Patent ID: 7048195
Filing Date: 2006-05-23
Classification: G04F,G06K

Abstract:
1. A method for expiring a device containing a time cell, the method comprising: performing a programming operation, wherein the programming operation sets a predetermined time period for the time cell; discharging a stored electrostatic charge in a charge storage element in the time cell, wherein the time cell has a substantially discharged state before the programming operation and has a controlled discharge state after the programming operation, and wherein the time cell transitions after the programming operation from the controlled discharge state to the substantially discharged state within the predetermined time period after the programming operation; reading a state of the time cell; generating a signal from the state of the time cell, wherein the signal indicates whether or not the predetermined time period has elapsed since the time cell was programmed; and in response to the signal indicating that the predetermined time period has elapsed, expiring the device; wherein the charge storage element in the time cell includes a floating gate field effect transistor; wherein the floating gate field effect transistor is configured within the time cell such that the floating gate field effect transistor turns on in response to applying power to the time cell after the predetermined time period has elapsed; wherein turning on the floating gate field effect transistor causes the signal to be generated; wherein the time cell includes a first node, a second node, and a difference amplifier that is connected to the first node and second node; and wherein when power is applied to the time cell, the first node reaches a predetermined voltage, the second node reaches a voltage that is determined by an amount of charge stored in a floating gate of the floating gate field effect transistor, and the difference amplifier outputs a voltage that is a difference between the voltage of the first node and the voltage of the second node.