Browsing by Author "Cheng, C. C."

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Analysis and Realization of TLC or even QLC Operation with a High Performance Multi-times Verify Scheme in 3D NAND Flash memory
(2018-01-01)
Lu, C. C.
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Cheng, C. C.
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Chiu, H. P.
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Lin, W. L.
;
Chen, T. W.
Feasibility of multi-times verify (MTV) scheme on triple-level cell (TLC) and quad-level cell (QLC) operations of charge-trap storage 3D NAND memories is investigated comprehensively. Results reveal that random telegraph noise (RTN) and program noise are the major factors affecting lower (LB) and upper boundaries (HB) of Vt distribution, respectively. Enlargement of operation window and reduction of ECC usage with MTV scheme to mitigate RTN-induced LB tail are demonstrated on TLC and QLC operations. In addition, the impact of program noise on HB Vt under various process conditions and ISPP steps is studied experimentally and also explained by our Monte Carlo simulator. Finally, program performance and reserved margin with and without MTV scheme applied on TLC and QLC operation are demonstrated.
Grain Boundary Trap-Induced Current Transient in a 3-D NAND Flash Cell String
(2019-04-01)
Lin, Wei-Liang
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Tsai, Wen-Jer
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Cheng, C. C.
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Ku, S. H.
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Liu, Lenvis
Transient cell current caused by the trapping/detrapping of grain boundary traps in the polycrystalline silicon (poly-Si) channel of a 3-D NAND cell string is comprehensively studied in this paper. This transient has a time constant of 10 mu s or longer and is strongly dependent on the bias history. It is also affected by the trap distribution as revealed by TCAD simulations. Sensing offset between program verify and read results in "pseudo" charge loss/gain that reduces the sensing margin. The posttreatment of the poly-Si channel is suggested to mitigate this effect.
Hot-Carrier Injection-Induced Disturb and Improvement Methods in 3D NAND Flash Memory
(2019-01-01)
Lin, Wei-Liang
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Tsai, Wen-Jer
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Cheng, C. C.
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Lu, Chun-Chang
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Ku, S. H.
We investigate a hot-carrier injection- induced program disturb in a 3D NAND flash memory. As there exist specific coding patterns, a "down-coupling" region and a "pre-charge" regions are formed during program-verify and the following program phases, respectively, in the inhibit cell strings. A high heating field is built nearby the PGM wordline. Hot carriers may inject into the inhibit cells as Vpgm is applied. Soft ramp-down and pre-turn-on schemes are proposed to mitigate this disturb.
Investigation of hot carrier degradation modes in LDMOS by using a novel three-region charge pumping technique
(2006)
Cheng, C. C.
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Tu, K. C.
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Wang, Tahui
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Hsieh, T. H.
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Tzeng, J. T.
Hot carrier stress induced oxide degradation in n-LDMOS is investigated by using a novel three-region charge pumping technique. This technique allows us to locate oxide damage area in various stress modes and gain insight into trap creation properties. Our characterization shows that a max. I(g) stress causes a largest drain current and subthreshold slope degradation because of both interface trap (N(it)) generation in the channel region and negative bulk oxide charge (Q(ox)) creation in the bird's beak region. The density of N(it) and Q(ox) can be separately extracted from the proposed charge pumping method. A numerical device simulation is performed to confirm our result.
LAND SUBSIDENCE USING ABSOLUTE AND RELATIVE GRAVIMETRY: A CASE STUDY IN CENTRAL TAIWAN
(2010-01-01)
Hwang, Cheinway
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Cheng, Tze-Chiang
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Cheng, C. C.
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Hung, W. C.
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土木工程學系
We experiment with absolute and relative gravimetry, to determine land subsidence. A gravin, network in the Yunlin County of central Taiwan is established to determine gravity variations that are largely due to land subsidence. Every 6 months, gravity values at two absolute gravity stations were measured by a FG5 gravimeter and those at 7 relative stations by a Graviton-EG and a Scintrex CG-5 relative gravimeter A weighted constraint network adjustment was carried out by holding fixed gravity values at the absolute stations. Correction models for temporal gravity changes are developed and applied to raw gravity measurements. The adjusted gravity values oscillate, but in general increase with time, showing signature of land subsidence. An empirical gravity-to-height admittance factor is determined using gravity change (from FG5) and height change (from levelling) at the two absolute gravity stations. At most gravity stations, there is good agreement between subsidence rates from gravimetry and levelling. Some large discrepancies (> 1 cm/year) also exist and am, caused by uncertainties in relative gravity accuracy, hydrological effects and the admittance factor This study suggests that gravimetry has the potential to determine land subsidence to cm accuracy and is more efficient and economic than tools such as levelling and GPS.
Polycrystalline-Silicon Channel Trap Induced Transient Read Instability in a 3D NAND Flash Cell String
(2016-01-01)
Tsai, Wen-Jer
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Lin, W. L.
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Cheng, C. C.
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Ku, S. H.
;
Chou, Y. L.
Vt instability caused by grain-boundary trap (GBT) in the poly-crystalline silicon (poly-Si) channel of a 3D NAND string are comprehensively studied. Experimental results reveal that trapping/detrapping of GBT would cause transient cell current with a time constant of lOus or longer, and this transient is strongly affected by the bias history. Sensing offset between program/erase verify (PV/EV) and read (RD) results in "pseudo" charge loss/gain that reduces the sensing margin. Modified EV, PV, or RD bias schemes are suggested to mitigate this effect.