Retention Loss Mechanisms Research Articles

Role of Al doping in the filament disruption in HfO2 resistance switches

Resistance switching devices, whose operation is driven by formation (SET) and dissolution (RESET) of conductive paths shorting and disconnecting the two metal electrodes, have recently received great attention and a deep general comprehension of their operation has been achieved. However, the link between switching characteristics and material properties is still quite weak. In particular, doping of the switching oxide layer has often been investigated only for looking at performance upgrade and rarely for a meticulous investigation of the switching mechanism. In this paper, the impact of Al doping of HfO2 devices on their switching operations, retention loss mechanisms and random telegraph noise traces is investigated. In addition, phenomenological modeling of the switching operation is performed for device employing both undoped and doped HfO2. We demonstrate that Al doping influences the filament disruption process during the RESET operation and, in particular, it contributes in preventing an efficient restoration of the oxide with respect to undoped devices.

Why Is FE–HfO2More Suitable Than PZT or SBT for Scaled Nonvolatile 1-T Memory Cell? A Retention Perspective

The limited retention time for single-transistor memory cell based on ferroelectric-gated field-effect-transistor (FeFET) has prevented the commercialization of its nonvolatile memory (NVM) option using the commercially available ferroelectric materials, such as strontium bismuth tantalite (SBT) or lead zirconium titanate (PZT), as the gate dielectric. However, the recent advent of the HfO2-based ferroelectric has demonstrated the strong possibility of meeting the NVM requirement of 10-year retention on aggressively scaled FeFETs. This letter will analyze why the retention for HfO2-based ferroelectric (FE–HfO2) is much longer than its PZT or SBT counterparts, based on the two major retention loss mechanisms: depolarization field and charge trapping.

A 250 mV Cu/SiO2/W Memristor with Half-Integer Quantum Conductance States.

Memristive devices, whose conductance depends on previous programming history, are of significant interest for building nonvolatile memory and brain-inspired computing systems. Here, we report half-integer quantized conductance transitions G = (n/2) (2e(2)/h) for n = 1, 2, 3, etc., in Cu/SiO2/W memristive devices observed below 300 mV at room temperature. This is attributed to the nanoscale filamentary nature of Cu conductance pathways formed inside SiO2. Retention measurements also show spontaneous filament decay with quantized conductance levels. Numerical simulations shed light into the dynamics underlying the data retention loss mechanisms and provide new insights into the nanoscale physics of memristive devices and trade-offs involved in engineering them for computational applications.

Effect of Al doping on the retention behavior of HfO2 resistive switching memories

The retention behavior of HfO2-based resistive switching memory cells (RRAM) is characterized as a function of Al doping concentration, which was previously reported to be a viable method for the improvement of the switching uniformity. While the low resistance state (LRS) does not exhibit any major variation up to 106s for all the tested devices, two retention loss mechanisms can be identified for the high resistance state (HRS). The main HRS trend follows a temperature-activated gradual decrease of the resistance, which also depends on the doping concentration. In addition, tail bits of the population distribution show a very fast retention loss process that strongly depends on the doping concentration.

Comparison of changes in retentive force of three stud attachments for implant overdentures.

PURPOSEThe aim of this study was to compare the changes in retentive force of stud attachments for implant overdentures by in vitro 2-year-wear simulation.MATERIALS AND METHODSThree commercially available attachment systems were investigated: Kerator blue, O-ring red, and EZ lock. Two implant fixtures were embedded in parallel in each custom base mounting. Five pairs of each attachment system were tested. A universal testing machine was used to measure the retentive force during 2500 insertion and removal cycles. Surface changes on the components were evaluated by scanning electron microscopy (SEM). A Kruskal-Wallis test, followed by Pairwise comparison, was used to compare the retentive force between the groups, and to determine groups that were significantly different (α<.05).RESULTSA comparison of the initial retentive force revealed the highest value for Kerator, followed by the O-ring and EZ lock attachments. However, no significant difference was detected between Kerator and O-ring (P>.05). After 2500 insertion and removal cycles, the highest retention loss was recorded for O-ring, and no significant difference between Kerator and EZ lock (P>.05). Also, Kerator showed the highest retentive force, followed by EZ lock and O-ring, after 2500 cycles (P<.05). Based on SEM analysis, the polymeric components in O-ring and Kerator were observed to exhibit surface wear and deformation.CONCLUSIONAfter 2500 insertion and removal cycles, all attachments exhibited significant loss in retention. Mechanism of retention loss can only be partially explained by surface changes.

Study of charge loss mechanisms for nano-sized localized trapping SONOS memory devices

Data retention loss mechanisms in nano-sized localized trapping polysilicon–oxide–nitride–oxide–silicon (SONOS) memory devices were investigated. To study the influence of charge lateral distribution on data retention, we used three channel hot electron injection (CHEI) programming operations with different substrate biases and same erasing operations to obtain three different charge profiles in the nitride layer after successive program/erase cycling. As a result, the mismatch profile of injected electrons and holes leads to serious degradation of data retention for the negative substrate biased CHEI programming. The experimental results suggest that the residual holes accumulation due to the mismatched profile, evidenced by the charge pumping and sub-threshold slope measurement, could be one of main origins of charge loss for nano-sized cycled SONOS cells. When the mismatch of the injected electrons and holes profiles is very serious after cycling, the accumulated holes detrapping by Frenkel–Poole emission and the lateral transport in the nitride layer may be an important data loss mechanism.

Wear simulation effects on overdenture stud attachments

The aim of this study was to evaluate wear effects on overdenture resilient attachments. Six commercially available attachments were investigated: ERA orange and white (EO and EW), Locator pink, white and blue (LRP, LRW and LRB) and OP anchor (OP). Five specimens were used for wear simulation while other two specimens served as controls. Fifteen thousands insertion-removal cycles were simulated. Dimensional changes and surface characteristics were evaluated using light microscopy and SEM, respectively. Sudden decrease of retentive force was characteristic for EO and EW attachments. Retentive force of Locator attachments fluctuated throughout the wear simulation period. Dimensional changes and surface wear was more expressed on plastic cores than on plastic rings of attachment males. Based on SEM analysis, some of the specimens obtained smoother surface after wear simulation. Mechanism of retention loss of resilient overdenture attachments can be only partially explained by dimensional changes and surface alterations.

Interface states formation in a localized charge trapping nonvolatile memory device

Two NROM nonvolatile memory devices that are practically identical but exhibit different postcycling characteristics are investigated. Electrical characterizations combined with two-dimensional drift diffusion simulations were employed to quantify and differentiate the retention loss mechanisms. The comparison demonstrates the coexistence of two retention loss mechanisms, lateral charge transport in the nitride layer, and hot carrier induced interface states formation and anneal. The fabrication conditions in the various studies reported in the literature and the resultant impact on interface states formation are most likely the cause of the formally nonresolved debate regarding the origin of retention loss in NROM technology. The reduction in interface state formation during cycling is a key to achieving high reliability NROM cells and products.

Unified retention model for localized charge trapping nonvolatile memory device

Retention after cycling in an NROM nonvolatile memory cell is investigated. Electrical characterizations combined with two-dimensional simulations were employed. By combining subthreshold current characterizations with gate-induced drain leakage measurements, the retention loss mechanisms are quantified and differentiated. A unified retention model for the NROM technology is proposed, incorporating both lateral charge transport in the nitride layer and hot carrier-induced interface-states formation. The fabrication conditions in the various studies reported in the literature and the resultant impact on interface-states formation are most likely the cause of the formally nonresolved debate regarding the origin of retention loss in NROM technology.

Root Cause of Charge Loss in a Nitride-Based Localized Trapping Memory Cell

Data retention loss mechanisms in nitride-based localized trapping memory devices are investigated with various electrical measurements and Medici simulations. First, the effect of program and erase cycles on device behavior is determined in terms of bottom oxide degradation and nitride charge profile evolution. Even if a strong degradation of the interface is observed, there is no important impact of this degradation on the cell behavior. However, the nitride charge profile evolves with cycling and leads to a three-pole electron-hole-electron profile over the channel region. Second, the interface trap annealing, the tunneling through the bottom oxide, and the lateral redistribution are studied in order to determine which mechanism plays the main role in the threshold voltage shift after cycling. The retention performance is dominated by a lateral redistribution of charges in the nitride layer.

Mechanism of retention loss when C 8 and C 18 HPLC columns are used with highly aqueous mobile phases

We describe investigations into the cause of retention losses encountered when C 8 and C 18 HPLC columns are used with highly aqueous (>90% water) mobile phases. A procedure for quantifying these losses is described, involving stopping and restarting the flow. This procedure was used to study the dependence of retention loss on the pore size, surface concentration, and chemical structure of the bonded phase. Experiments were also carried out to determine how to restore the original retention of the columns by changing the composition of the mobile phase, or by increasing the pressure applied to the column. The results are shown to be consistent with a mechanism based on the theory of pore filling by non-wetting liquids, as employed in Mercury Porosimetry. The retention losses are attributed to the highly aqueous mobile phase being forced out of the pores when the flow is stopped and the pressure released. Retention is lost because the mobile phase is no longer in contact with the interior surface of the particles, where most of the surface area is located. The implications of this phenomenon for maximizing the reversed phase retention of polar analytes are discussed.

Si–H Bond Breaking Induced Retention Degradation During Packaging Process of 256 Mbit DRAMs With Negative Wordline Bias

Data retention degradation of a 256-Mbit DRAM during the packaging process is investigated in this paper. Electrical measurement and device simulation show that a trap-assisted leakage degrades the retention time even in packaging process at about 250/spl deg/C. Retention time of the degraded chip is strongly dependent on the negative wordline voltage and operation temperature, but less sensitive to the substrate bias. Trap-assisted gate induced drain leakage is proposed as the mechanism of retention loss in the degraded chip. The degraded chips usually can be repaired by another thermal baking process. We propose Si-H bond breaking and the subsequent trap generation at the gate and drain overlap region as the root cause of retention degradation according to the fact that the Si-H bond density of backend passivation oxide and nitride layers correlate well with the retention performance of DRAM chips with negative wordline bias. Moreover, the packaged chip shows variable retention behavior during a thermal baking of 250/spl deg/C. Theoretical calculation indicates that the trap generation or movement to the high electrical field region beneath the gate can increase the trap-assisted gate induced drain leakage by about an order of magnitude.

Nanoscale Properties of SrBi2Ta2O9 Thin Films

AbstractPiezoresponse scanning force microscopy (PFM) was applied to study the nanoscale mechanism of retention loss in SrBi2Ta2O9 (SBT) thin films. Experiments were conducted by performing local polarization reversal within an individual grain with subsequent imaging of a resulting domain structure at different time intervals. The retention behavior of the films was studied as a function of switching conditions and electrode material. SFM was also used for nanoscale mapping of leakage current sites and investigation of electrical conduction mechanism at these sites. For the first time, the development of dielectric breakdown in SBT films was directly observed at nanoscale.

Nanoscale Investigation of Polarization Retention Loss in Ferroelectric Thin Films VIA Scanning Force Microscopy

ABSTRACTScanning force microscopy (SFM) was applied to direct nanoscale investigation of the mechanism of retention loss in ferroelectric thin films. Experiments were conducted by performing local polarization reversal within an individual grain with subsequent imaging of a resulting domain structure at various time intervals. A conductive SFM tip was used for domain switching and imaging in the SFM piezoresponse mode.