Browsing by Author "Wu, Jau-Yi"

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A Novel Varying-Bias Read Scheme for MLC and Wide Temperature Range TMO ReRAM
(2016-11)
Lin, Yu-Hsuan
;
Lee, Ming-Hsiu
;
Wu, Jau-Yi
;
Lin, Yu-Yu
;
Lee, Feng-Ming
Resistance of transition metal oxide (TMO) resistive random access memory (ReRAM) depends sharply on temperature, resulting in drastic memory window loss at high temperature. Thus, it is difficult to design the ReRAM that can serve a wide range of operating conditions. It is especially challenging to achieve multi-level-cell (MLC) ReRAM because of the large temperature dependency. This letter investigates both the temperature and read bias dependencies of WOx ReRAM, and found both can be well understood by a modified space-charge limited conduction model. Using this model, we have designed a novel read scheme that varies the read bias according to the device temperature and compensates for the temperature effect on cell resistance. Since TMO ReRAM devices depend on defect states, cell-to-cell and cycle-to-cycle variations are naturally large. An algorithm is designed to address the variability. A 1-Mb WOx ReRAM array is fabricated to both characterize the bias and temperature dependencies and verify the new read scheme. A large and constant memory window is preserved for MLC across a wide temperature range (-40 degrees C-125 degrees C), suitable for high-reliability applications.
A Resistance Drift Compensation Scheme to Reduce MLC PCM Raw BER by Over 100x for Storage Class Memory Applications
(2017-01)
Khwa, Win-San
;
Chang, Meng-Fan
;
Wu, Jau-Yi
;
Lee, Ming-Hsiu
;
Su, Tzu-Hsiang
For multilevel cell (MLC) phase change memory (PCM), resistance drift ( R-drift) phenomenon causes cell resistance to increase with time, even at room temperature. As a result, the fixed-threshold-retention (FTR) raw-bit-error-rate (RBER) surpasses practical ECC correction ability within hours after being programmed. This study proposes a resistance drift compensation (RDC) scheme to mitigate R-drift issue. The proposed RDC scheme realizes PCM drift compensation and features RDC pulse to suppress ECC decoding failure. The proposed approach was validated using a 90-nm 128M cells PCM chip and an FPGA-based memory controller verification system. The MLC PCM FTR RBER has been suppressed by over 100x, thereby bringing it within ECC capability. The effectiveness of the RDC scheme was verified up to 106 cycles.
A Resistance Drift Compensation Scheme to Reduce MLC PCM Raw BER by Over 100x for Storage Class Memory Applications
(2017-01)
Khwa, Win-San
;
Chang, Meng-Fan
;
Wu, Jau-Yi
;
Lee, Ming-Hsiu
;
Su, Tzu-Hsiang
For multilevel cell (MLC) phase change memory (PCM), resistance drift ( R-drift) phenomenon causes cell resistance to increase with time, even at room temperature. As a result, the fixed-threshold-retention (FTR) raw-bit-error-rate (RBER) surpasses practical ECC correction ability within hours after being programmed. This study proposes a resistance drift compensation (RDC) scheme to mitigate R-drift issue. The proposed RDC scheme realizes PCM drift compensation and features RDC pulse to suppress ECC decoding failure. The proposed approach was validated using a 90-nm 128M cells PCM chip and an FPGA-based memory controller verification system. The MLC PCM FTR RBER has been suppressed by over 100x, thereby bringing it within ECC capability. The effectiveness of the RDC scheme was verified up to 106 cycles.
A Resistance-Drift Compensation Scheme to Reduce MLC PCM Raw BER by Over 100x for Storage-Class Memory Applications
(2016)
Khwa, Win-San
;
Chang, Meng-Fan
;
Wu, Jau-Yi
;
Lee, Ming-Hsiu
;
Su, Tzu-Hsiang
Excellent Resistance Variability Control of WOx ReRAM by a Smart Writing Algorithm
(2016)
Lin, Yu-Hsuan
;
Wu, Jau-Yi
;
Lee, Ming-Hsiu
;
Wang, Tien-Yen
;
Lin, Yu-Yu
TMO ReRAMs, being built on defect states, are intrinsically subject to variability. In this work, cell to cell variability is studied by applying write shots with different current and voltage for Forming, SET and RESET operation, respectively. We found the keys to eliminate tail bits consist of (1) longer write pulse, (2) higher write current and (3) higher write voltage. In order to optimize the performance of write speed, write power and device reliability, we developed a novel resistance control method using a smart writing algorithm. Compared to the conventional ISPP writing scheme, this smart writing algorithm covers much wider switching condition variability and cell-to-cell variation by controlling both current and voltage for ReRAM operation.