TiN Device Research Articles

Role of interfacial layer on complementary resistive switching in the TiN/HfOx/TiN resistive memory device

The role of the bottom interfacial layer (IL) in enabling stable complementary resistive switching (CRS) in the TiN/HfOx/IL/TiN resistive memory device is revealed. Stable CRS is obtained for the TiN/HfOx/IL/TiN device, where a bottom IL comprising Hf and Ti sub-oxides resulted from the oxidation of TiN during the initial stages of atomic-layer deposition of HfOx layer. In the TiN/HfOx/Pt device, where formation of the bottom IL is suppressed by the inert Pt metal, no CRS is observed. Oxygen-ion exchange between IL and the conductive path in HfOx layer is proposed to have caused the complementary bipolar switching behavior observed in the TiN/HfOx/IL/TiN device.

Effect of Stoichiometry of TiN Electrode on the Switching Behavior of TiN/HfOx/TiN Structures for Resistive RAM

ABSTRACTTwo types of TiN/HfOx/TiN devices have been fabricated where the top 200nm TiN electrode has been deposited by two different sputtering methods; reactive, using a titanium target in a nitrogen environment, and non-reactive, using a titanium nitride target. Characterization of the materials shows that the reactive TiN is single-phase stoichiometric TiN with a sheet resistance of 7Ω/square. The non-reactive TiN has a sheet resistance of 300Ω/square and was found to contain significant amounts of oxygen. The resistive switching behavior differs for both devices. The reactive stoichiometric TiN device results in bipolar switching with a Roff/Ron ratio of 50. The non-reactive TiN results in unipolar switching with a Roff/Ron ratio of more than 103, however this device shows poor reproducibility. These results show that an oxygen rich layer between the top electrode and insulator affects the Roff value. It supports the theory of oxygen vacancies leading to the formation of conductive filaments.

Unipolar resistive switching behavior in Pt/HfO2/TiN device with inserting ZrO2 layer and its 1 diode-1 resistor characteristics

Transition of resistive switching (RS) behavior from bipolar to unipolar is observed in Pt/ZrO2/HfO2/TiN device. Due to the lower oxygen vacancy concentration of the HfO2 layer, formation/rupture of the conducting filament is confined in the HfO2 layer. To fulfill one diode and one resistor (1D1R) structure, the electrical relation between the RS device and diode is investigated. A Pt/InZnO/CoO/Pt/TiN oxide diode is fabricated to provide enough forward current and large forward/reverse current ratio to achieve unipolar RS behavior. The 1D-1R structure with Pt/ZrO2/HfO2/TiN resistive random access memory shows robust retention and nondestructive readout property at 85 °C.

Record Mobility in Transparent p-Type Tin Monoxide Films and Devices by Phase Engineering

Here, we report the fabrication of nanoscale (15 nm) fully transparent p-type SnO thin film transistors (TFT) at temperatures as low as 180 °C with record device performance. Specifically, by carefully controlling the process conditions, we have developed SnO thin films with a Hall mobility of 18.71 cm(2) V(-1) s(-1) and fabricated TFT devices with a linear field-effect mobility of 6.75 cm(2) V(-1) s(-1) and 5.87 cm(2) V(-1) s(-1) on transparent rigid and translucent flexible substrates, respectively. These values of mobility are the highest reported to date for any p-type oxide processed at this low temperature. We further demonstrate that this high mobility is realized by careful phase engineering. Specifically, we show that phase-pure SnO is not necessarily the highest mobility phase; instead, well-controlled amounts of residual metallic tin are shown to substantially increase the hole mobility. A detailed phase stability map for physical vapor deposition of nanoscale SnO is constructed for the first time for this p-type oxide.

Polarity Reversion of the Operation Mode of HfO<SUB>2</SUB>-Based Resistive Random Access Memory Devices by Inserting Hf Metal Layer

The reversion of polarity within bipolar resistive switching operation occurs in Pt/HfO2/TiN and Pt/Hf/HfO2/TiN resistive random access memory devices. This reversion of voltage polarity is the result of interface generation which induces a conduction mechanism transformation from Poole-Frenkel emission to space charge limited current mechanism. To prove the reversion of polarity, this study uses curve fitting of I-V relations to verify the conduction mechanism theoretically and physical analysis to verify the oxygen ion distribution practically. The proposed Pt/Hf/HfO2/TiN devices exhibit good resistive switching characteristics, such as good uniformity, low voltage operation, robust endurance (10(3) dc sweep), and long retention (3 x 10(4) s at 85 degrees C).

Resistive switching behavior of a CeO2 based ReRAM cell incorporated with Si buffer layer

We propose a novel resistive switching device with a W/CeO2/Si/TiN structure by incorporating a very thin Si buffer layer in the interface, the memory performance of this device such as forming voltage, operation power, and window and endurance characteristics were found to be remarkably improved compared with the performance of the device without the Si layer. This improvement was attributed to the formation of Ce-silicate and thus proper introduction of oxygen vacancies at the interface. The gradual reset process of the W/CeO2/Si/TiN device under sweeping voltage was quantitatively analyzed by parallel conductive filaments model. Our results provide a guideline for the operation voltage control for further optimizing device performance and give new insights into the gradual reset process.

Experimental investigation of the reliability issue of RRAM based on high resistance stateconduction

In this paper, reliability issues of robustHfOx-based RRAM are experimentally investigated in terms of cycling ageing, temperatureimpact and voltage acceleration. All reliability issues can be estimated by the conduction ofthe high resistance state (HRS). The conduction current of the HRS exponentiallyincreases as the square root of the applied voltage, which is well explained by‘quasi-Poole–Frenkel-type’ trap assistant tunneling. Further experiments on HRS conductionat different temperatures show that the depth of the potential well of the trap inHfOx film is about 0.31 eV. The degradation induced by the cycling ageing ispossibly ascribed to the increase of the amount of oxygen ions in theTiOx layer ofthe TiN/TiOx/HfOx/TiN device. The retention times with various stress voltages at different temperatures alsoexhibit an exponential relationship to the square root of the applied voltage, indicatingthat stress current plays a dominant role for the degradation of the HRS. Anoxygen-release model is proposed to explain the relationship of retention time to HRSconduction current.

On the role of Ti adlayers for resistive switching in HfO2-based metal-insulator-metal structures: Top versus bottom electrode integration

The authors demonstrate bipolar resistive switching in TiN/HfO2/Ti(top)/TiN devices using a (Bi) complementary metal-oxide semiconductor (CMOS) compatible technology process. The device performance includes a cycling endurance in dc sweeping mode >103. The results suggest that HfO2-based metal-insulator-metal devices with Si CMOS compatible metal electrodes may be well suited for future embedded nonvolatile memory applications. However, hysteretic current-voltage characteristics were only observed for a Ti top adlayer, whereas a Ti bottom adlayer integration did not show any resistive switching effect. Using x-ray photoelectron spectroscopy, the authors examined the interface chemistry of the Ti/HfO2 interface. It is clearly observed that Ti top adlayer deposition results in an increased nitrogen- and oxygen-gettering activity in contrast to Ti bottom adlayer. It follows that the formation of a nonstoichiometric HfO2 layer at the Ti/HfO2 interface is crucial for resistive switching.

Improved Stress Reliability of Analog Metal–Insulator–Metal Capacitors Using $\hbox{TiO}_{2}/\hbox{ZrO}_{2}$ Dielectrics

We have studied the stress reliability of high-kappa Ni/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiN metal-insulator-metal capacitors under constant-voltage stress. The increasing TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness on ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> improves the 125- <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C leakage current, capacitance variation (Delta <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> ), and long-term reliability. For a high density of 26 fF/mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , good extrapolated ten-year reliability of small Delta <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> ~ 0.71% is obtained for the Ni/10-nm-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /6.5-nm- ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / TiN device at 2.5-V operation.

Electrical evidence of unstable anodic interface in Ru∕HfOx∕TiN unipolar resistive memory

Unipolar resistive switching behaviors of Ru∕HfOx∕TiN devices with Ru as anode were investigated. Wide dispersion of switching operation parameters was observed. The conduction mechanisms in low and high resistance states of the devices were characterized to be Ohmic-like and tunneling, respectively. The band offset of the Ru∕HfOx interface was extracted from the measured tunneling current versus voltage characteristics. Instability of the band offset at the anodic interface was observed and may be responsible for the wide fluctuation of the operation voltage in the Ru∕HfOx∕TiN device at a high resistance state. The possible mechanism for these unstable characteristics of band offset at the Ru∕HfOx interface is also discussed.

High speed resistive switching in Pt∕TiO2∕TiN film for nonvolatile memory application

We have fabricated and investigated the bipolar resistive switching characteristics of Pt/rutile-TiO2∕TiN devices for resistance memory applications. Data writing for five-level resistance states has been demonstrated by varying the amplitude of 5ns voltage pulses. In addition, data retention of more than 256h at 85°C and an excellent endurance of over 2×106cycles have been confirmed. These results indicate that Pt∕TiO2∕TiN devices have a potential for nonvolatile multiple-valued memory devices.

Relationship between work function of indium tin oxide and device performances of C60 modified organic light-emitting diodes

Relationships between the work function of indium tin oxide (ITO) and device performances of C60 modified organic light-emitting diodes were investigated. The work function of ITO was controlled by changing the degree of oxidation of ITO using ultraviolet/O3 treatment. High efficiency could be obtained in the C60 modified device with short ITO treatment time, while driving voltage was lowered in the C60 modified device with long ITO treatment time.

CuPc/C60 Solar Cells–Influence of the Indium Tin Oxide Substrate and Device Architecture on the Solar Cell Performance

We investigated the influence of different indium tin oxide (ITO) surface treatments on the performance of organic solar cells with different device architectures. Two types of devices (CuPc in contact with ITO treated with different treatments and C60 in contact with ITO treated with different treatments) were fabricated. The surfaces of CuPc and C60 layers deposited on ITO substrates treated with different surface treatments were examined using atomic force microscopy. The devices were characterized by measuring current-voltage characteristics in the dark and under AM1 illumination. We found that a one order of magnitude improvement in the AM1 power conversion efficiency for ITO/CuPc/C60/Al cells can be achieved for optimal ITO surface treatment, while ITO/C60/CuPc/Cu devices exhibit less sensitivity to surface treatments. Moreover, these devices exhibit better performance compared to ITO/CuPc/C60/Al devices. The observed differences in sensitivity to surface treatments were attributed to difference in the dependence of the film surface on ITO surface morphology for CuPc and C60.