PolySi-SiO 2 -ZrO 2 -SiO 2 -Si Flash Memory Incorporating a Sol-Gel-Derived ZrO 2 Charge Trapping Layer

In this paper, we propose a method for depositing the charge trapping layer of a high-k polySi-SiO 2 -ZrO 2 -SiO 2 -Si ͑SOZOS͒ memory device. In this approach, the trapping layer was formed through simple two steps: ͑i͒ spin-coating of the ZrCl 4 precursor and ͑ii͒ rapid thermal annealing for 1 min at 900°C under an oxygen atmosphere. The morphology of the ZrO 2 charge trapping layer was confirmed through X-ray photoemission spectroscopy analysis. The sol-gel-derived layer exhibited improved charge trapping in the SOZOS memory device, resulting in a threshold voltage shift of 2.7 V in the I d -V g curve, P/E ͑program/erase͒ speeds as fast as 0.1 ms, good data retention up to 10 4 s ͑only a 5% charge loss due to deep trapping in the ZrO 2 layer͒, and good endurance ͑no memory window narrowing after 10 5 P/E cycles͒. © 2006 The Electrochemical Society. ͓DOI: 10.1149/1.2337846͔ All rights reserved. The first floating-gate ͑FG͒ nonvolatile semiconductor memory was invented by Sze and Kahng in 1967. 1 Conventional FG memory uses polysilicon as a charge-storage layer surrounded by the dielectric. 2 Although floating-gate structures can achieve high densities and good program/erase ͑P/E͒ speeds and exhibit good reliability in portable flash memory devices, there are concerns regarding the ability to scale up their production. 3 When the tunneling oxide thickness is below 10 nm, the storage charge in the FG leaks readily because defects form in the tunneling oxide after repeated write-erase cycles or through direct tunneling of the current. PolySi-oxide-nitride-oxide-silicon ͑SONOS͒ memory devices have been studied recently as an approach to solving the issue of scaling FG memory. 3 Because of their spatially isolated deep-level traps, SONOS memories exhibit better charge retention than do FG memories that have a bitcell tunneling oxide layer thinner than 10 nm. As a result, a single defect in the tunneling oxide will not cause the discharge of the memory cell. 3 SONOS memory devices use silicon nitride as a charge trapping layer; the conduction band offset between the tunneling oxide and nitride is 1.05 eV. When a positive voltage is applied on the gate, the band bends downward so that the electrons in the Si subconduction band will tunnel through the tunneling oxide and a portion of the nitride will become trapped in the charge trapping layer. Before they become trapped in the nitride, the electrons must tunnel through a portion of the nitride, which degrades the program speed. In addition, because the conduction band offset of the nitride is only 1.05 eV, back tunneling of the trapped electron may also occur. To solve these problems, high-k materials are potential candidates to replace the traditional silicon nitride as the charge trapping layer. The advantages of using high-k materials are the larger band offset with the tunneling oxide and the greater number of trapping sites than those found in silicon nitride. For an HfO 2 high-k material, the conduction band offset between the tunneling oxide and HfO 2 is 1.6 eV. When programming, the electron will tunnel through a shorter distance in HfO 2 than in the nitride to become trapped. This feature can be exploited to achieve high P/E speeds. Thus, it will be beneficial to use a high-k material as the charge trapping layer in a SONOS-type memory device, provided that there are many deep-level trapping sites in the high-k material. Many technologies have been developed recently for the deposition of high-k layers onto tunneling oxides, 7-10 including atomic layer deposition ͑ALD͒, metallorganic chemical vapor deposition ͑MOCVD͒, and physical vapor deposition ͑PVD͒. In the ALD method, ZrCl 4 and H 2 O are used to prepare the ZrO 2 films. For the PVD process, a zirconium metal target is used for sputtering under ambient oxygen to deposit the ZrO 2 films. In the CVD method, ZrCl 4 is used as a precursor to deposit ZrO 2 films. Recently, we proposed the first so-called sol-gel spin-coating method for the deposition of the thin film. 11 Sol-gel spin-coating methods use metal halides hydrolyzed in organic or colloidal solvents to form precursor compounds that undergo hydrolysis, condensation, and polymerization to form metal-oxide networks. The advantages of using sol-gel methods to fabricate high-k films are that they are cheaper than ALD, PVD, and MOCVD approaches, and that various types of thin films can be synthesized. To the best of our knowledge, sol-gel spin-coating of a high-k film has yet to be reported for the preparation of charge trapping layers for flash memory devices. In this paper, we describe the fabrication of a polySi-SiO 2 -ZrO 2 -SiO 2 -Si ͑SOZOS͒ flash memory device prepared through the deposition of ZrCl 4 using the sol-gel spin-coating method and subsequent rapid thermal annealing ͑RTA͒. We performed physical and electrical analyses, including X-ray photoemission spectroscopy ͑XPS͒, I d -V g , retention, and P/E speed measurements, to evaluate the performance of the sol-gel ZrO 2 films for their potential use as charge trapping layers in SOZOS memory devices. Experimental ZrCl 4 ͑99.5%, Aldrich, USA͒ was used as the synthetic precursor of the zirconia. A mother sol solution was first prepared by dissolving ZrCl 4 in isopropanol ͑IPA; Fluka; water content Ͻ0.1%͒ under vigorous stirring in an ice bath. The sol solution was obtained by fully hydrolyzing ZrCl 4 with a stoichiometric quantity of water in IPA to yield a Zr:IPA molar ratio of 1:1000. The fabrication of the sol-gel spin-coated SOZOS memory began with LOCOS isolation process on p-type 150 mm silicon ͑100͒ substrate. At first, a 4 nm tunneling oxide layer was grown thermally at 925°C through furnace oxidation. The Zr:IPA solution ͑molar ratio: 1:1000͒ was coated using a spin-coater at 3000 rpm for 60 s at 25°C. A TEL Clean Track model-MK8 ͑Japan͒ spin-coater was used. The as-deposited thin film was initially baked at 200°C for 10 min to perform densification, followed by high-k RTA for 1 min in an O 2 atmosphere to form the ZrO 2 charge trapping layer. The film thickness, measured using an ellipsometer, was 10 nm. A 30 nm thick blocking oxide was deposited using high-density-plasmaenhanced chemical vapor deposition ͑HDPCVD͒, followed by deposition of a poly-Si gate ͑200 nm͒. After gate deposition, the following processes were applied to fabricate the SOZOS memory: * Electrochemical Society Active Member.

Measurement of Total Free Iron in Soils by H2S Chemisorption and Comparison with the Citrate Bicarbonate Dithionite Method

Free iron is one of the major analytical items for soil basic properties. It is also an important indicator for understanding the genesis of soil, soil classification, and soil distribution behavior. In this study, an alternative analytical method (chemisorption) based on thermodynamic knowledge was proposed for measurement of total free iron oxides in soils. Several representative soil samples belonging to alfisols, ultisols, inceptisols, and entisols were collected from Taiwan and tested by the chemisorption, and the estimated total free iron oxides were compared with those measured from the traditional citrate bicarbonate dithionite (CBD) method. Experimental results showed that the optimal operating temperature was found to be at 773 K and the carbon monoxide (CO) is the best gaseous reagent to promote the formation of FeS. The estimated total free iron oxides for soil samples determined from the chemisorption in the presence of CO were very close to those from the CBD technique. The result of regression indicates that the estimated total free iron is strongly correlated with the CBD-Fe content (R2=0.999) in the presence of CO

Seroepidemiology of dengue virus infection among adults during the ending phase of a severe dengue epidemic in southern Taiwan, 2015

Abstract Background A severe dengue epidemic occurred in 2015 which resulted in over 22,000 laboratory-confirmed cases. A cross-sectional seroprevalence study was conducted during the ending phase of this epidemic to evaluate the true incidence of dengue virus (DENV) infection and the level of herd immunity. Methods Adult residents in three administrative districts with high dengue incidence were recruited; workers in two districts with intermediate dengue incidence were also recruited for comparison. DENV-specific IgM and IgG were tested using commercial enzyme-linked immunosorbent assays. DENV RNA was detected using commercial quantitative real-time reverse transcriptase polymerase chain reaction assay. Univariate and multivariate logistic regressions were performed to identify risk factors for recent and past DENV infection. Results The overall seroprevalence of anti-DENV IgM and IgG in 1391 participants was 6.8 and 17.4%, respectively. The risk of recent DENV infection increased with age, with the elderly having the highest risk of infection. Living in areas with high incidence of reported dengue cases and having family members being diagnosed with dengue in 2015 were also independent risk factors for recent DENV infection. One sample was found to have asymptomatic viremia with viral load as high as 105 PFU/ml. Conclusions Comparing the seroprevalence of anti-DENV IgM with the incidence of reported dengue cases in 2015, we estimated that 1 out of 3.7 dengue infections were reported to the surveillance system; widespread use of rapid diagnostic tests might contribute to this high reporting rate. The results also indicate that the overall herd immunity remains low and the current approved Dengvaxia® is not quite suitable for vaccination in Taiwan

Dual dimeric interactions in the nucleic acid-binding protein Sac10b lead to multiple bridging of double-stranded DNA

Nucleoid-associated proteins play a crucial role in the compaction and regulation of genetic material across organisms. The Sac10b family, also known as Alba, comprises widely distributed and highly conserved nucleoid-associated proteins found in archaea. Sac10b is identified as the first 10 kDa DNA-binding protein in the thermoacidophile Sulfolobus acidocaldarius. Here, we present the crystal structures of two homologous proteins, Sac10b1 and Sac10b2, as well as the Sac10b1 mutant F59A, determined at a resolution of 1.4–2.0 Å. Electron microscopic images reveal the DNA-bridging capabilities of both Sac10b1 and Sac10b2, albeit to varying extents. Analyses of crystal packing and electron microscopic results suggest that Sac10b1 facilitates cooperative DNA binding, forming extensive bridged filaments via the conserved R58 and F59 residues at the dimer-dimer interface. Substitutions at R58 or F59 of Sac10b1 attenuate end-to-end association, resulting in non-cooperative DNA binding, and formation of small, bridged DNA segments in a way similar to Sac10b2. Analytical ultracentrifuge and circular dichroism confirm the presence of thermostable, acid-tolerant dimers in both Sac10b1 and Sac10b2. These findings attest to the functional role of Sac10b in organizing and stabilizing chromosomal DNA through distinct bridging interactions, particularly under extreme growth conditions

The AMPK Agonist AICAR Inhibits TGF-β1 Induced Activation of Kidney Myofibroblasts

<div><p>Activation of interstitial myofibroblasts and excessive production of extracellular matrix proteins are common pathways that contribute to chronic kidney disease. In a number of tissues, AMP-activated kinase (AMPK) activation has been shown to inhibit fibrosis. Here, we examined the inhibitory effect of the AMPK activator, 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR), on renal fibrosis <i>in</i><i>vivo</i> and TGF-β1-induced renal fibroblasts activation <i>in</i><i>vitro</i>. A unilateral ureteral obstruction (UUO) model was induced in male BALB/c mice. Mice with UUO were administered AICAR (500 mg/Kg/day) or saline intraperitoneally 1 day before UUO surgery and daily thereafter. Both kidneys were harvested 7 days after surgery for further analysis. For the in vitro studies, NRK-49F rat fibroblasts were pre-incubated with AICAR before TGF-β1 stimulation. The inhibitory effects of AICAR on signaling pathways down-stream of TGF-β1 were analyzed. In UUO model mice, administration of AICAR attenuated extracellular matrix protein deposition and the expression of α-smooth muscle actin (α-SMA), type I collagen and fibronectin. Pre-incubation of NRK-49F cells with AICAR inhibited TGF-β1-induced myofibroblast activation. Silencing of AMPKα1 by siRNA or by blocking AMPK activation with Compound C diminished the inhibitory effect of AICAR. Moreover, the inhibitory effects of AICAR on TGF-β1-mediated myofibroblast activation were associated with down-regulation of ERK 1/2 and STAT3. Our results suggest that AICAR reduces tubulointerstitial fibrosis in UUO mice and inhibits TGF-β1-induced kidney myofibroblast activation. AMPK activation by AICAR may have therapeutic potential for the treatment of renal tubulointerstitial fibrosis.</p></div

The AMPKα1 subunit is the target of the inhibitory effects of AICAR in TGF-β1-stimulated NRK-49F cells.

<p>Cultured NRK-49F cells were transfected with specific siRNA for AMPKα1 (10 nM, 100 nM) or AMPKα2 (10 nM, 100 nM) or a control siRNA for 24 h. After 24 h of incubation, transfected cells were pre-incubated with or without AICAR (0.5 mM) for 30 mins. Then, these cells were stimulated with TGF-β1 (1 ng/mL) for 24 h before harvesting. (A) The inhibitory effects of siAMPKα1 were evaluated by measuring phospho-AMPKα and total-AMPKα levels. Representative immunoblots from three independent experiments are shown. (B) The efficiency of different concentrations of siAMPKα1 (1 nM, 10 nM, 50 nM, 100 nM) on AMPKα1 mRNA expression were evaluated. Data are expressed relative to the expression in control cells without transfection. Each bar represents the mean ± S.E. of three independent experiments. *<i>P</i><0.05 versus the TGF-β1 group; #<i>P</i><0.05 versus the TGF-β1+ AICAR group; ##<i>P</i><0.05 versus the control group. C: control, T: TGF-β1, A: AICAR.</p

AICAR reduces the expression of α-smooth muscle actin (α-SMA), collagen I, and fibronectin.

<p>A unilateral ureteral obstruction (UUO) model was induced in adult male BALB/c mice. Sham animals had their kidney exposed but the ureter was not tied. Mice with UUO were administered intra-peritoneal AICAR (500 mg·kg⁻¹·day) or saline 1 day before the UUO surgery and daily thereafter. Obstructed kidneys were harvested 7 days after surgery. qPCR analysis of the mRNA expression of collagen I (A), fibronectin (B), TGF-β1 (C), TNF-α (D) and MCP-1 (E), in sham, UUO, and UUO + AICAR kidneys. Data are expressed relative to the expression in sham-operated kidneys. Kidney tissue lysates were also subjected to immunoblot analysis with specific antibodies against α-SMA, collagen I, fibronectin, and β-actin (F). Protein expression levels of α-SMA (G), collagen I (H) and fibronectin (I) were analyzed by western blotting, quantified by densitometry, and normalized to β-actin levels. Each bar represents the mean ± S.E. (n = 6 in each group). *<i>P</i><0.05 between the sham and UUO group; #<i>P</i><0.05 between the UUO and UUO + AICAR group.</p

The effects of AICAR on the inhibition TGF-β1-mediated kidney myofibroblast activation were associated with STAT3 down-regulation.

<p>Cultured NRK-49F cells were incubated with TGF-β1 (1 ng/mL) for 15 mins–180 mins in the presence or absence of AICAR (0.5 mM). (A) Cell lysates were subject to immunoblot analysis with antibodies against phospho-STAT3 (P-STAT3) and tubulin. (B) TGF-β1-induced α-smooth muscle actin (α-SMA) expression in NRK-49F cells is inhibited by JAK inhibitor and AICAR. Representative immunoblots from three experiments are shown. Each bar represents the mean ± S.E. of three independent experiments. *<i>P</i><0.05 versus the corresponding group (control or TGF-β1) at the same time duration after TGF-β1 treatment; #<i>P</i><0.05 versus the control group; ##<i>P</i><0.05 versus the TGF-β1 group. C: control, T: TGF-β1, A: AICAR.</p