Yu Chi Chang

Resistive Switching Behavior in Gelatin Thin Films for Nonvolatile Memory Application

This paper presents the characteristics of gelatin, which can cause reproducible resistive switching and bipolar resistive switching in aluminum (Al)/gelatin (35 nm)/ITO devices. The memory devices exhibited a high ON/OFF ratio of over 10(6) and a long retention time of over 10(5) seconds. The resistive switching mechanism was investigated using the high-angle dark field transmission electron microscopy image of Al/gelatin/ITO devices in the pristine high-resistance state (HRS) and then in returning to HRS after the RESET process. The energy-dispersive X-ray spectroscopy analysis revealed the aggregation of N and Al elements and the simultaneous presence of carbon and oxygen elements in the rupture of filament paths. Furthermore, via a current-sensing atomic force microscopy, we found that conduction paths in the ON-state are distributed in a highly localized area, which is associated with a carbon-rich filamentary switching mechanism. These results support that the chelation of N binding with Al ions improves the conductivity of the low-resistance state but not the production of metal filaments.

Solution-processed Al-chelated gelatin for highly transparent non-volatile memory applications

Using the biomaterial of Al-chelated gelatin (ACG) prepared by sol-gel method in the ITO/ACG/ITO structure, a highly transparent resistive random access memory (RRAM) was obtained. The transmittance of the fabricated device is approximately 83% at 550 nm while that of Al/gelatin/ITO is opaque. As to the ITO/gelatin/ITO RRAM, no resistive switching behavior can be seen. The ITO/ACG/ITO RRAM shows high ON/OFF current ratio (>105), low operation voltage, good uniformity, and retention characteristics at room temperature and 85 °C. The mechanism of the ACG-based memory devices is presented. The enhancement of these electrical properties can be attributed to the chelate effect of Al ions with gelatin. Results show that transparent ACG-based memory devices possess the potential for next-generation resistive memories and bio-electronic applications.

Multilayered Barium Titanate Thin Films by Sol-Gel Method for Nonvolatile Memory Application

The modification of multispin casting multilayered barium titanate (BTO) thin films on indium tin oxide (ITO)/glass substrate without doping other elements is adopted to improve the memory performance. The X-ray photoelectron spectroscopy analysis reveals the concentration of oxygen vacancies can be reduced by the increasing number of the BTO layer. Mechanisms of conducting paths relating to the concentration of oxygen vacancies will also be explicated. The memory devices showed typical bipolar resistive switching behavior and an ON/OFF ratio of over 106. The memory devices also exhibited outstanding uniformity. A retention time of over 105 s without fluctuation at room temperature and 85 °C can be achieved.

High-Mobility Pentacene-Based Thin-Film Transistors With Synthesized Strontium Zirconate Nickelate Gate Insulators

Strontium zirconate nickelate [(SZN); Sr0.69Ni0.47Zr0.085O3.75] was synthesized through a sol-gel method by adding nickel (II) acetylacetone instead of titanium isopropoxide, which can effectively make thin films smoother and further act as gate insulators applied in pentacene-based thin-film transistors. Sol-gel SZN thin films were investigated by X-ray photoelectron spectroscopy and atomic force microscopy to confirm the chemical composition and smooth surface roughness, and the latter property was found to be compatible for pentacene thin film growth. Thus, the electrical characteristics of pentacene-based transistors exhibited a high mobility of 10.04 cm2 V-1s-1 low threshold voltage of -1.51 V,, and low subthreshold swing slope of 350 mV/decade. To realize high mobility mechanisms, intermolecular coupling and reorganization energy of pentacene thin films were introduced. Another purpose of this introduction was to evaluate the higher hopping rate of carriers between the adjacent pentacene molecules on SZN derived from the March-Hush equation than other high-κ traditional sol-gel insulators.

Bipolar Resistive Switching Behavior in Sol-Gel MgTiNiO x Memory Device

High-resistance state (HRS) current has significant effect on the reliability and power consumption of resistive switching memories. Low HRS current is helpful for obtaining ultra-low power and for high ON/OFF ratio nonvolatile memory application. The reduced HRS current of a sol-gel magnesium titanate nickelate-based resistive random access memory by using nickel (II) acetylacetone as substitute for acetylacetone in magnesium titanate (MTO) was presented. Forming-free, high ON/OFF ratio of over 106, excellent current distribution and good retention at 85 °C were achieved. Moreover, the effect of nickel (Ni) on the surface roughness, operation voltage, switching cycles, HRS current, ON/OFF ratio, current distribution, and switching behavior was explored. These results indicate that the incorporation of Ni in sol-gel MTO is an effective way to achieve high-performance memory devices.

Phonon-assisted stimulated emission from pendeoepitaxy GaN stripes grown on 6H-SiC substrates

Phonon-assisted stimulated emission has been demonstrated by photopumping GaN stripes grown via pendeoepitaxy on 6H-SiC (0001) substrates. Transverse-electric-polarized emission with well-defined Fabry-Perot modes located at one longitudinal optical phonon energy (90meV) below the band gap of GaN was observed at 77K. An effective refractive index of 8.578 was obtained using a cavity length of 13.3μm and a mode spacing of 0.6nm. This value is significantly higher than the value previously reported in the literature using ellipsometry, which indicates that the absorption loss is more severe during lasing when the excess carrier concentration is very high.

Bipolar resistive switching behavior with high on/off ratio of transparent mgtiniox films

The bipolar resistive switching (BRS) characteristics in the magnesium titanate nickelate (MTN) films synthesized by the sol-gel method have been investigated. The BRS characteristics without forming process are fitted by the ohmic transport and the F-P emission mechanism. The ON/OFF current ratio is more than 108, better than other perovskite films. In addition, the titanium (Ti) atom combines the bidentate ligands of nickel (II) acetylacetone to form the compound Ti acetylacetone chelate, which further improves the moisture resistivity of MTN films and maintains a coefficient of variation (CV) of less than 30% after 28 d under an atmospheric environment. Furthermore, good retention properties (two different resistance states can be maintained at a ratio of 106 up to 105 s at 85°C) are observed. Given its thermal stability and good performance, MTN is a promising candidate for use in memory devices.

Resistive switching properties of alkaline earth oxide-based memory devices

A reduced high-resistance state (HRS) current assists in obtaining high ON/OFF ratio and is beneficial to operation flexibility. This study proposes that less difference in the atomic radius of alkaline earth oxide-based memory devices is beneficial to reduce the HRS current. Forming-free resistive-switching behavior in the alkaline earth oxide-based memory device using magnesium titanate (MTO), strontium titanate (STO), and barium titanate (BTO) thin films is fabricated by sol-gel method. The dependence of HRS current on the difference in atomic radius was predicted by the Hume–Rothery rule and confirmed experimentally. The hydrolyzed particles, surface roughness, and density of oxygen vacancy were decreased when the difference in atomic radius between the Ti element and alkaline earth metal was less. Compared with the BTO thin film, the MTO thin film has fewer particles, smoother surface, and less density of oxygen vacancy, resulting in lower HRS current. Thus, suitable element selection for the alkaline earth oxide-based memory devices can reduce the HRS current.

1T1R nonvolatile memory with Al/TiO2/Au and Sol-Gel-processed insulator for barium zirconate nickelate gate in pentacene thin film transistor

A one-transistor and one-resistor (1T1R) architecture with a resistive random access memory (RRAM) cell connected to an organic thin-film transistor (OTFT) device is successfully demonstrated to avoid the cross-talk issues of only one RRAM cell. The OTFT device, which uses barium zirconate nickelate (BZN) as a dielectric layer, exhibits favorable electrical properties, such as a high field-effect mobility of 2.5 cm2/Vs, low threshold voltage of −2.8 V, and low leakage current of 10−12 A, for a driver in the 1T1R operation scheme. The 1T1R architecture with a TiO2-based RRAM cell connected with a BZN OTFT device indicates a low operation current (10 μA) and reliable data retention (over ten years). This favorable performance of the 1T1R device can be attributed to the additional barrier heights introduced by using Ni (II) acetylacetone as a substitute for acetylacetone, and the relatively low leakage current of a BZN dielectric layer. The proposed 1T1R device with low leakage current OTFT and excellent uniform resistance distribution of RRAM exhibits a good potential for use in practical low-power electronic applications.

Effects of Ni in Strontium Titanate Nickelate Thin Films for Flexible Nonvolatile Memory Applications

This paper investigated the performance of flexible resistive random access memory devices based on simple spin-coated sol–gel-derived strontium titanate nickelate (STN) thin films on polyethylene terephthalate substrate. A high on/off ratio of