Patent ID: 7242239
Filing Date: 2007-07-10
Classification: G11C

Abstract:
1. A circuit operable to program an electrically alterable element to a programmed state and determine whether said electrically alterable element is in the programmed state or not, comprising: a multiple conduction state field effect transistor (“multi-state FET”) having a source, a drain, and a gate operable to control conduction between said source and said drain, at least one of said source or said drain being coupled to said electrically alterable element to apply a current to said electrically alterable element, said FET having a first threshold voltage and a second threshold voltage effective at the same time as said first threshold voltage, said gate being operable to control operation of said multi-state FET in multiple states including a) an essentially nonconductive state when a gate-source voltage applied between said gate and said source does not exceed said first threshold voltage and does not exceed said second threshold voltage such that a source-drain current between said source and said drain is at most negligible; b) a first conductive state when said gate-source voltage exceeds said first threshold voltage and does not exceed said second threshold voltage such that said source-drain current has a first operating value when said multi-state FET operates in saturation; and c) a second conductive state when said gate-source voltage exceeds said first threshold voltage and said second threshold voltage such that said source-drain current has a second operating value at least about ten times larger than said first operating value; and a control circuit operable to i) set said gate-source voltage to a magnitude greater than said second threshold voltage to cause said multi-state FET to conduct said source-drain current having said second operating value as a programming current to alter said electrically alterable element from an unprogrammed state to a programmed state, ii) set said gate-source voltage to a magnitude between said first threshold voltage and said second threshold voltage to operate said multi-state FET in said first conductive state to determine whether or not said electrically alterable element is in said programmed state by determining an amount of said source-drain current conducted through said electrically alterable element by said multi-state FET when said multi-state FET is in said first conductive state.