Active solid-state devices (e.g. – transistors – solid-state diode – Bulk effect device – Bulk effect switching in amorphous material
Reexamination Certificate
2001-06-30
2004-06-08
Pert, Evan (Department: 2829)
Active solid-state devices (e.g., transistors, solid-state diode
Bulk effect device
Bulk effect switching in amorphous material
C365S163000
Reexamination Certificate
active
06747286
ABSTRACT:
FIELD
Programmable devices, including phase change memory devices that can be programmed by modifying the state of a phase change material.
BACKGROUND
Typical computers, or computer related devices, include physical memory, usually referred to as main memory or random access memory (RAM). Generally, RAM is memory that is available to computer programs and read-only memory (ROM) is memory that is used, for example, to store programs that boot a computer and perform diagnostics. Typical memory applications include dynamic random access memory (DRAM), static random access memory (SRAM), erasable programmable read-only memory (EPROM), and electrically erasable programmable read-only memory (EEPROM).
Solid state memory devices typically employ micro-electronic circuit elements for each memory bit (e.g., one to four transistors per bit) in memory applications. Since one or more electronic circuit elements are required for each memory bit, these devices may consume considerable chip “real estate” to store a bit of information, which limits the density of a memory chip. The primary “non-volatile” memory element of these devices, such as an EEPROM, typically employ a floating gate field effect transistor device that has limited re-programmability and which holds a charge on the gate of field effect transistor to store each memory bit. These classes of memory devices are also relatively slow to program.
Phase change memory devices use phase change materials, i.e., materials that can be electrically switched between a generally amorphous and a generally crystalline state, for electronic memory application. One type of memory element originally developed by Energy Conversion Devices, Inc. of Troy, Mich. utilizes a phase change material that can be, in one application, electrically switched between a structural state of generally amorphous and generally crystalline local order or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states. Typical materials suitable for such application include those utilizing various chalcogenide elements. These electrical memory devices typically do not use field effect transistor devices as the memory storage element, but comprise, in the electrical context, a monolithic body of thin film chalcogenide material. As a result, very little chip real estate is required to store a bit of information, thereby providing for inherently high density memory chips. The state change materials are also truly non-volatile in that, when set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until reprogrammed as that value represents a physical state of the material (e.g., crystalline or amorphous). Thus, phase change memory materials represent a significant improvement in non-volatile memory.
One characteristic common to solid state and phase change memory devices is significant power consumption particularly in setting or reprogramming memory elements. Power consumption is significant, particularly in portable devices that rely on power cells (e.g., batteries). It would be desirable to decrease the power consumption of a memory device.
Another characteristic common to solid state and phase change memory devices is limited reprogrammable cycle life from/to an amorphous and crystalline state. Further, over time the phase change material can fail to reliably reprogram from/to an amorphous and a crystalline state. It would be desirable to increase the programmable cycle life of the phase change memory material.
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Hwang, Y.N., Hong, J.S., Lee, S.H., Ahn, S.J., Jeong, G.T., Koh, G.H., Kim, H.J., Jeong, W.C., Lee, S.Y., Park, J.H., Ryoo, K.C.., Horii, H., Ha, Y.H., Yi, J.H., Cho, W.Y., Kim, Y.T., Lee, K.H., Joo, S.H., Park, S.O., Jeong, U.I., Jeong, H.S. and Kim, Kinam, “Completely CMOS-Compatible Phase-Change Nonvolatile RAM Using NMOS Cell Transistors,” presented at 2003 19thIEEE Non-Volatile Semiconductor Memory Workshop, Monterey, California, Feb. 26-20, 2003.
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Ovonyx Inc.
Pert Evan
Trop Pruner & Hu P.C.
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