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In this article, for the first time, a variation of lateral doping (VLD) technique was proposed to improve blocking voltage and ON-resistance properties in the lateral β-Ga2O3 metal–oxide–semiconductor field-effect transistor (MOSFET). Enhancement-mode operation was achieved in the VLD transistor. The maximum transconductance of this new device is more than three times as large as the uniformly doped (UD) transistor. Moreover, the OFF-state electric field at the channel was suppressed compared to the UD transistor, resulting in higher blocking voltage. We also investigated the optimal device properties with changing channel concentration in the drift region of VLD transistor. A power figure of merit of 332.7 MW/cm2 was reached by VLD design. Thus, this proposed structure provides a new design strategy for high-power β-Ga2O3 MOSFETs. [ABSTRACT FROM AUTHOR]

This work reports a $\beta $ -Ga2O3 double-barrier Schottky barrier diode (DBSBD) with both low turn-on voltage and low reverse leakage current by using Ni and PtOx as the anode electrode. The barrier height of PtOx-based diode can be effectively modulated from 1.26 to 1.62 eV by adjusting oxygen pressure during sputtering processes. Combining the maximum work function of PtOx electrode with the optimization of the electrode ratio of Ni and PtOx, the DBSBD with an electrode diameter ratio of $\text{D}_{\text {Ni}} /\text{D}_{\text {PtOx}}= {75}/{150} \mu \text{m}$ not only exhibits a high forward current of 470.9 A/cm2 (at 3.5 V), a low on-resistance of 4.1 $\text{m}\Omega ~\cdot $ cm2 and a low turn-on voltage of 1.13 V, but also possesses a relatively low reverse leakage current of ${1.2}\times {10}^{-{7}}$ A/cm2 (at −100 V), which is more than one order of magnitude lower than that of the Ni-SBD. Silvaco TCAD simulation reveals that such optimization can be attributed to the suppression of edge leakage current due to the double-barrier contact. Therefore, the strategy of double-barrier design can balance the forward and reverse characteristics in SBD, providing a new device structure for advanced power electronics. [ABSTRACT FROM AUTHOR]

In this letter we present a high performance $\varepsilon $ -Ga2O3 solar-blind photodetector (SBPD) with asymmetric Schottky electrodes. The $\varepsilon $ -Ga2O3 films were heteroepitaxially grown on ${c}$ -plane sapphire by metal-organic chemical vapor deposition (MOCVD). The SBPDs were fabricated in the form of lateral interdigitated Schottky electrodes composed of a Pt/Ti/Au metal stack and a Ti/Au metal stack. The SBPD shows a rectification ratio of ~ 102 with low dark current of 25 pA at ${V} = {6}$ V. A high photo-to-dark-current ratio of ${5.7}\boldsymbol {\times }{10}^{{4}}$ under 254 nm light illumination was measured. Furthermore, the SBPD exhibits an ultrahigh detectivity and external quantum efficiency of ${4.2}\boldsymbol {\times }{10}^{{14}}$ Jones and ${4.1}\boldsymbol \,\,{\times }\,\,{10}^{{4}}$ %, respectively. Most importantly, the SBPD possesses an ultrahigh responsivity of 84 A/W with a fast response speed of 100 ms, suggesting the promise of $\varepsilon$ -Ga2O3 in the future photodetector applications. [ABSTRACT FROM AUTHOR]

$\alpha $ -phase-dominated Ga2O3 films were hete- roepitaxially grown on ${c}$ -plane sapphire substrate by metal-organic chemical vapor deposition (MOCVD), followed by the fabrication of ultraviolet (UV) photodetectors (PDs) with a metal-semiconductor-metal (MSM) structure using a Ti/Au metal stack as the electrode in an interdigitated geometry. The PDs possess a record low dark current of 81 fA under a bias voltage of 12 V, with a high sensitivity as confirmed by a record high photo-to-dark-current ratio exceeding 107 under 254 nm light illumination. Furthermore, the PDs also exhibit a high responsivity and the photoconductive gain of 11.5 A/W and 55, respectively. Most importantly, it shows an ultrahigh detectivity of ${1.0} \times {10}^{{15}}$ Jones with a quite fast response of 42ms, paving the way for advancement of next-generation PD applications. [ABSTRACT FROM AUTHOR]

The self-rectifying resistive-switching (RS) device is one of the most promising solutions to overcome the sneaking current issue in a 3D vertical crossbar array. In this letter, we report a CMOS-compatible, forming-free, self-rectifying resistive random access memory device with high uniformity and low operation voltage (<3V) for embedded memory application. Thanks to the low read voltage, this device shows robust read disturbance (>109) characteristics. After introducing a 3-nm HfO2 thin film between Pd and WOx layer, Schottky contact of Pd/HfO2 was formed, which resulted in rectifying property. The HfO2 layer also served as an oxygen reservoir for RS in WOx layer. This novel memory device with excellent performance is a promising candidate for future high density embedded memory application. [ABSTRACT FROM AUTHOR]

Negative-SET behavior, induced by nano-filament overgrowth phenomenon, takes major responsibility to the reset failure phenomenon in conductive bridge random access memory (CBRAM). The unexpected negative-SET behavior in CBRAM devices can result in serious reliability issues and has been an obstacle on the way to mass production. In this letter, we have proposed a back-end-of-line (BEOL) compatible TiN barrier layer to improve the device reliability in CBRAM devices by eliminating the nano-filament overgrowth phenomenon and negative-SET behavior. Thus, a higher reset voltage can be applied to the TiN barrier layer devices to achieve more complete reset process and obtain better resistive switching performance. The results show that the Cu/HfO2/TiN/Ru device with one transistor structure has excellent comprehensive memory properties, including high reliability, fast switching speed, high resistance state uniformity, high endurance, long retention, and multi-level storage ability. [ABSTRACT FROM PUBLISHER]

Uniformity and retention are crucial aspects for application of conductive bridge random access memory. In this letter, a self-aligned CuSiN interfacial layer was inserted into Cu/TaOx/Ru device to obtain a Cu/CuSiN/ TaOx/Ru structure. Compared with the Cu/TaOx/Ru device, the Cu/CuSiN/TaOx/Ru device shows much improved uniformity of resistance and programming voltage. Higher ON/ OFF ratio of $1000\times $ was observed, benefiting from the tight distribution of resistance. The standard deviation of set voltage was minimized from 0.635 to 0.187. Moreover, the low-resistance-state retention was also greatly improved. The uniformity and retention improvement could be well explained by the good controlment of cation injection and localization induced by CuSiN interfacial layer. [ABSTRACT FROM AUTHOR]

In this letter, we dynamically investigate the resistive switching characteristics and physical mechanism of the Ni/ZrO2/Pt device. The device shows stable bipolar resistive switching behaviors after forming process, which is similar to the Ag/ZrO2/Pt and Cu/ZrO2/Pt devices. Using in situ transmission electron microscopy, we observe in real time that several conductive filaments are formed across the ZrO2 layer between Ni and Pt electrodes after forming. Energy-dispersive X-ray spectroscopy results confirm that Ni is the main composition of the conductive filaments. The ON-state resistance increases with increasing temperature, exhibiting the feature of metallic conduction. In addition, the calculated resistance temperature coefficient is equal to that of the 10-30 nm diameter Ni nanowire, further indicating that the nanoscale Ni conductive bridge is the physical origin of the observed conductive filaments. The resistive switching characteristics and the conductive filament's component of Ni/ZrO2/Pt device are consistent with the characteristics of the typical solid-electrolyte-based resistive random access memory. Therefore, aside from Cu and Ag, Ni can also be used as an oxidizable electrode material for resistive random access memory applications. [ABSTRACT FROM AUTHOR]

With recent progress in material science, resistive random access memory (RRAM) devices have attracted interest for nonvolatile, low-power, nondestructive readout, and high-density memories. Relevant performance parameters of RRAM devices include operating voltage, operation speed, resistance ratio, endurance, retention time, device yield, and multilevel storage. Numerous resistive-switching mechanisms, such as conductive filament, space-charge-limited conduction, trap charging and discharging, Schottky Emission, and Pool-Frenkel emission, have been proposed to explain the resistive switching of RRAM devices. In addition to a discussion of these mechanisms, the effects of electrode materials, doped oxide materials, and different configuration devices on the resistive-switching characteristics in nonvolatile memory applications, are reviewed. Finally, suggestions for future research, as well as the challenges awaiting RRAM devices, are given. [ABSTRACT FROM AUTHOR]

Resistive switching mechanism of zirconium oxide-based resistive random access memory (RRAM) devices composed of Cu-doped ZrO film sandwiched between an oxidizable electrode and an inert electrode was investigated. The Ag/ZrO:Cu/Pt RRAM devices with crosspoint structure fabricated by e-beam evaporation and e-beam lithography show reproducible bipolar resistive switching. The linear I- V relationship of low resistance state (LRS) and the dependence of LRS resistance ( R) and reset current ( I) on the set current compliance ( I) indicate that the observed resistive switching characteristics of the Ag/ZrO:Cu/Pt device should be ascribed to the formation and annihilation of localized conductive filaments (CFs). The physical origin of CF was further analyzed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). CFs were directly observed by cross-sectional TEM. According to EDS and elemental mapping analysis, the main chemical composition of CF is determined by Ag atoms, coming from the Ag top electrode. On the basis of these experiments, we propose that the set and reset process of the device stem from the electrochemical reactions in the zirconium oxide under different external electrical stimuli. [ABSTRACT FROM AUTHOR]

Resistive switching memory with low switching current is critical for low-power application. In this letter, we successfully demonstrated a four-terminal resistive RAM device with ultra-low switching current. The device is SET by one pair of electrodes and RESET by the other. The rupture process of conductive filament can be resulted from electrochemical reaction dominated by the lateral electric field. Therefore, during RESET process, no current flows through the filament, leading to an ultra-low switching current. [ABSTRACT FROM PUBLISHER]

Resistive switching with a self-rectifying feature is one of the most effective solutions to overcome the sneaking current issue in a crossbar structure. In this letter, we have successfully demonstrated a prototype device with inherent rectifying property with \a-Si/WO3 bilayer structure. After a forming process, the devices exhibit obvious rectifying property with forward/reverse current ratio of \10^2 at \pm0.75 V and excellent reproducibility. The formation of localized conductive filaments (CFs) in the \WO3 layer and the corresponding CF/a-Si Schottky contact are suggested to explain the rectifying behavior. The results in this letter demonstrate a possible way to realize selector-free crossbar structure. [ABSTRACT FROM AUTHOR]

Scaling is a key issue for resistive switching (RS) memory before commercialization. In this letter, we reveal the impact of electrode diffusion on the device performance as the thickness of RS material scaled. Serious deterioration of on/off ratio and device yield was observed when the material thickness scaled below 3 nm. A new method of two-step electrode deposition accompanied with reoxidization process was employed to overcome this problem. Significant improvements of device performance such as forming free, low RESET current (\sim\!\!\1\ \mu\A), high on/off ratio ( > 100), and 100% device yield were achieved thereafter. [ABSTRACT FROM PUBLISHER]

In this letter, current sweeping programming mode is proposed as an efficient method to improve the uniformity of the switching properties of resistive memory devices. Based on the measurement results of the reset process of filament-based \Cu/\HfO2/\Pt devices, current sweeping mode (CSM) can significantly reduce the distributions of Roff values, as compared with the standard voltage sweeping mode. The improvement is attributed to the elimination of the intermediate resistive states due to the positive feedback of joule heat generation by the use of current sweeping. Furthermore, the uniform distribution of the Vset values of the set process is also obtained by current sweeping, which stems from the localization of conductive filaments formation and rupture. CSM provides an effective way to achieve uniform resistance state of memory cell. [ABSTRACT FROM AUTHOR]

The metal oxide solid electrolyte-based RRAM device is a promising candidate for post-Flash nonvolatile memories. The critical operation of such a device is the reset process, and the reliability study of the reset process and its physical understanding are important to RRAM development. This letter reports the observation of the unstable reset behavior in the \ZrO2-based solid electrolyte RRAM. During the reset process, the LRS resistance (RL) of the device will first reduce and then increase to reach the HRS. It is also seen that V0 (i.e., the voltage at which a decrease of RL takes place) decreases with an increase of RL. This instability might be attributed to the subsequent growth of the filament after the energy barrier is reached to overcome electrochemical reactions during the reset process. Based on these experimental results, a physical model is developed to help explain the dependence of V0 on RL, which provides an important guideline to the optimization of RRAM operations. [ABSTRACT FROM PUBLISHER]

In this letter, the insertion of a Cu nanocrystal (NC) layer between the Pt electrode and \ZrO2 film is proposed as an effective method to improve resistive switching properties in the \ZrO2 -based resistive switching memory. This Cu/\ZrO2:Cu/Cu NC/Pt memory exhibits asymmetric nonpolar resistive switching behavior, low operating voltage ( < 1.2 V), low Reset current (< \50\ \mu\A), and high uniformity of resistance switching. The switching mechanism is believed to be related with the formation and rupture of conductive filament. The NC-induced electrical field enhancement has the benefit to accelerate and control the CF formation process, thus leading to low-switching threshold voltage and high uniformity. [ABSTRACT FROM PUBLISHER]

Resistive switching characteristics of ZrO2 films containing gold nanocrystals (nc-Au) are investigated for nonvolatile memory applications. The sandwiched top electrode/ZrO2 (with nc-Au embedded)/n+ Si structure exhibits two stable resistance states (high-resistance state and low-resistance state). By applying proper voltage bias, resistive switching from one state to the other state can be achieved. This resistive switching behavior is reproducible and the ratio between the high and low resistances can be as high as two orders. The intentionally introduced nc-Au in ZrO2 films can improve the device yield greatly. ZrO2 films with gold nanocrystals embedded are promising to be used in the nonvolatile resistive switching memory devices. [ABSTRACT FROM AUTHOR]

[Display omitted] Micro light-emitting diodes (Micro-LEDs) are currently attracting more and more attention. Thin film transistors (TFTs) with micron channel lengths can be used to drive Micro-LEDs. The key parameters of TFTs, such as mobility, I ON /I OFF and threshold voltage, still need to be improved. In this study, we propose and experimentally demonstrate ZnO TFTs using bilayer electrodes to overcome the short channel effects when the channel length is scaled down to 3 μm. Ti, Mo and Sn interlayers not only serve as diffusion barriers to prohibit migration of Cu atoms from the top electrodes, but also enhance adhesive energy of the metal electrodes on ZnO channel layers. ZnO TFTs using Cu/Ti bilayer electrodes exhibit the best performance, e.g., a high mobility of 45.3 cm2V-1s−1, a high I ON /I OFF ratio of 4.28 × 109, a low subthreshold of 0.24 V/dec and a proper threshold voltage of 1.13 V. The high mobility can be attributed to a significant decrease of the barrier height and a slight narrowing of the space charge layer, and the high ratio of I ON /I OFF is concerned with the high electron concentration under an ON-state condition. Thus, ZnO TFTs using Cu/Ti bilayer electrodes can be used in next-generation displays. [ABSTRACT FROM AUTHOR]