Apparatus and method for programming a one-time programmable memory device

#The invention relates generally to integrated circuit memory devices and specifically to a method and apparatus for programming one-time programmable non-volatile memory devices.

#Memory devices for storing digital data are abundant in today's computers, automobiles, cell telephones and media information cards. Certain of these memory devices or storage elements, referred to as non-volatile memory, retain the stored digital data when power is removed from the device. For example non-volatile memory instructions instruct a computer during the boot-up process and store instructions and data for sending and receiving calls in a cellular telephone. Electronic products of all types, from microwave ovens to heavy industrial machinery, store their operating instructions in these non-volatile storage elements. Certain non-volatile memory devices offer multiple programming capabilities, with previously stored information overwritten by new data. Other non-volatile devices provide only one-time programmability.

#Another class of memory devices, volatile memory devices, looses the stored information when power is removed. Dynamic random access memories (DRAM) and static random access memories (SRAM) are two types of volatile storage elements.

#The foregoing and other features of the invention will be apparent from the following more particular description of the invention, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

#FIG. 1 is a prior art circuit for blowing one-time programmable fuses.

#FIG. 2A is a schematic representation of a three terminal thyristor and FIG. 2B is a cross-sectional view of a thyristor formed in an integrated circuit.

#Before describing in detail the particular method and apparatus for programing one-time programmable fuses according to the present invention, it should be observed that the present invention resides primarily in a novel and non-obvious combination of elements and process steps. Accordingly, the inventive features have been represented by conventional elements and process steps in the figures, showing only those specific details that are pertinent to the present invention so as not to obscure the disclosure with details that will be readily apparent to those skilled in the art having the benefit of the description herein.

#A thyristor (also referred to as a silicon-controlled rectifier, SCR) is a four-layer pnpn device having three or four terminals, an anode, a cathode, and one or two gates. A three terminal thyristor 23 is illustrated schematically in FIG. 2A. When an anode 24 (connected to an anode terminal 24A) is held positive with respect to a cathode 25 (having a cathode terminal 25A), a relatively short duration and relatively low magnitude trigger current pulse applied to a gate 26 (via a gate terminal 26A) causes the thyristor to turn on to conduct current between the anode 24 and cathode 25. In this conducting state, the thyristor behaves as a rectifier. Conduction continues even after the trigger current on the gate terminal 26A is reduced to zero. The thyristor turns off only when the current flowing between the anode 24 and the cathode 25 falls below a holding current value. Since current is carried through the material bulk rather than through a surface region as in a MOSFET, thyristors generally have higher current ratings than MOSFETs.

#A four terminal thyristor 27, comprising a second gate 28 (and a gate terminal 28A) is illustrated in FIG. 3. Triggering the thyristor 27 into the on state can be assisted by pulsing the gate terminal 28A with a current of opposite polarity to the current pulse applied to the gate 26. Thyristor operation using one or two gates is well known in the art.