Kenneth K. Hunt

Chalcogenide memory arrays: characterization and radiation effects

The chalcogenide material used for phase-change applications in rewritable optical storage (Ge/sub 2/Sb/sub 2/Te/sub 5/) has been integrated with a 0.5-/spl mu/m radiation-hardened CMOS process to produce 64-Kbit memory arrays. On selected arrays, electrical testing demonstrated up to 100% memory cell yield, 100-ns programming and read speeds, and write currents as low as 1 mA/bit. Devices functioned normally from -55/spl deg/C to 125/spl deg/C. Write/read endurance has been demonstrated to 1/spl times/10/sup 8/ before first bit failure. Total ionizing dose (TID) testing to 2 Mrad(Si) showed no degradation of chalcogenide memory element, but it identified a write current generator circuit degradation specific to the test chip, which can be easily corrected in the next generation of array and product. Static single-event effects (SEE) testing showed no effect to an effective linear energy transfer (LET/sub EFF/) of 98 MeV/mg/cm/sup 2/. Dynamic SEE testing showed no latchup or single-event gate rupture (SEGR) to an LET/sub EFF/ of 123 MeV/mg/cm/sup 2/. Two sensitive circuits, neither containing chalcogenide elements, and both with small error cross sections, were identified. The sense amp appears sensitive to transients when reading the high-resistance state. The write driver circuit may be falsely activated during a read cycle, resulting in a reprogrammed bit. Radiation results show no degradation to the hardened CMOS or effects that can be attributed to the phase-change material.

Nonvolatile, high density, high performance phase-change memory

An electrically reprogrammable resistor approach has been developed as a basis for a new nonvolatile memory that is potentially denser, faster, and easier to make than Dynamic RAM (DRAM). It relies on structural phase transitions induced by nanosecond-scale heating and cooling of small volumes of chalcogenide films within the memory cell. Initial target markets include FLASH memory, embedded memory, and DRAM.

Total dose radiation response and high temperature imprint characteristics of chalcogenide based RAM resistor elements

Chalcogenide thin film resistor elements are being integrated with CMOS structures for nonvolatile memory applications. This paper reports on the first total dose and imprint data published on this new technology demonstrating no observable effects on chalcogenide films after exposure to 1 Mrad(Si) and 125/spl deg/C temperature.

A 4-Mb Non-volatile Chalcogenide Random Access Memory designed for space applications: Project status update

BAE Systems, under contract to the US Air Force Research Labs, has been developing a 4Mb Non-Volatile Chalcogenide Random Access Memory (C-RAM¿) optimized for the radiation environments encountered in spacecraft applications. C-RAM is a phase change memory with a unique combination of features that collectively provide a high-density, low-power, non-volatile memory solution that is radiation hardened and meets rigorous reliability requirements. The device is now undergoing QML qualification in preparation for being flight production ready in early 2009. Flight qualified C- RAM will serve the critical need for rad hard non-volatile RAM in strategic space and military applications. Initial space radiation effects testing (heavy ion induced upset rates) demonstrate the robust nature of the device. No memory cell upsets were recorded and the majority of the observed upsets were soft errors (SE) induced in the sense amp circuits which are easily correctable with common error correcting code (ECC) algorithms. During the product development phase potential failure mechanisms associated with phase change memories such as proximity disturbs and drill-in effects were evaluated to determine whether they were legitimate concerns for C-RAM. These tests and other tests involving second order radiation effects, such as the effect of heavy ion radiation exposure on data retention lifetime were conducted. The results of these investigations further demonstrate the full capacity of the product technology. This paper will describe the C-RAM design and operation, and the results of the test and characterization of C-RAM devices.

Results of radiation effects on a chalcogenide non-volatile memory array

We report on the progress of a recent addition to non-volatile solid state memory technologies suited for space and other ionizing radiation environments. We summarize the material and processing science behind the current generation of chalcogenide phase-change memories fabricated on CMOS structures. The chalcogenide material used for phase-change applications in rewritable optical storage (Ge/sub 2/Sb/sub 2/Te/sub 5/) has been integrated with a radiation hardened CMOS process to produce 64 kbit memory arrays. On selected arrays electrical testing demonstrated up to 100% memory cell yield, 100 ns programming and read speeds, and write currents as low as 1 mA/bit. Devices functioned normally from -55/spl deg/C to 125/spl deg/C. Write/read endurance has been demonstrated to 1/spl times/10/sup 8/ before first bit failure. Radiation results show no degradation to the hardened CMOS or effects that can be attributed to the phase-change material. Future applications of the technology are discussed.

Characterization of the 4Mb chalcogenide-random access memory

The first generation of C-RAM memory is designed to greatly exceed (in density, write speed, endurance) the existing non-volatile memory solutions for space and to close the gap that exists between system requirements and availability. Based on the success of the 64kb C-RAM program, a 4Mb C-RAM prototype has been designed and fabricated in 0.25 mum radiation-hardened CMOS. In this paper we present a description of the 4Mb design as well as results of recent characterization and radiation test of the first pass of prototype parts

Progress on a New Non‐Volatile Memory for Space Based on Chalcogenide Glass

We report on the progress of a recent addition to non‐volatile solid state memory technologies suited for space and other ionizing radiation environments. We summarize the material and processing science behind the current generation of chalcogenide phase‐change memories fabricated on CMOS structures. The chalcogenide material used for phase‐change applications in rewritable optical storage (Ge2Sb2Te5) has been integrated with a radiation hardened CMOS process to produce 64kbit memory arrays. On selected arrays electrical testing demonstrated up to 100% memory cell yield, 100ns programming and read speeds, and write currents as low as 1mA/bit. Devices functioned normally from − 55°C to 125°C. Write/read endurance has been demonstrated to 1 × 108 before first bit failure. Radiation results show no degradation to the hardened CMOS or effects that can be attributed to the phase‐change material. Future applications of the technology are discussed.

Implications of the Logical Decode on the Radiation Response of a Multi-Level Cell NAND Flash Memory

The radiation response of a multi-level cell (MLC) NAND flash is used to determine the organization of logical states as they correspond to floating gate charge levels of constituent bit cell transistors. This “logical decode” is then used to demonstrate how an MLC device can be used to emulate a single-level cell (SLC) flash with total dose radiation sensitivity equivalent to and even surpassing that of a comparable actual SLC device. In addition, it is shown that the logical decode must be taken into account when performing radiation testing on MLC flash devices so as to gather accurate worst case response data.