Browsing by Author "Lee, Feng-Ming"

Now showing 1 - 3 of 3

A Comprehensive Study of 3-stage High Resistance State Retention Behavior for TMO ReRAMs from Single Cells to a Large Array
(2017-01-01)
Lin, Yu-Hsuan
;
Ho, Yung-Han
;
Lee, Ming-Hsiu
;
Wang, Chao-Hung
;
Lin, Yu-Yu
For the first time the retention of high resistance state (HRS) in resistive random access memory (ReRAM) is found to compose of three stages - extending tail-bits, distribution shift, and then distribution broadening. This work provides a comprehensive study on the HRS's retention behavior in WOx-based ReRAMs from single device characteristics to group distribution. Different from conventional activation energy (Ea) analysis, the mean and variance of the array distribution are presented to overcome the non-uniform Ea issue. Since the extracted Ea fits well with Vo(2+) (oxygen vacancy) migration characteristics, the three retention stages are suggested to be the competing results from the migration, recombination, and generation of the Vo(2+) and O2- in the gap region. A three-dimensional retention model with kinetic Monte Carlo simulator and trap-assisted tunneling conduction is proposed to discuss the dominating mechanism in different time and temperature scales. The mechanism for random telegraph noise is also included to illustrate the fluctuating nature of the HRS cells.
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.
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.