High-pressure Hydrogen Annealing Research Articles

High-pressure hydrogen annealing improving the cryogenic operation of Si (110)-oriented n-MOSFETs

High-pressure hydrogen annealing improving the cryogenic operation of Si (110)-oriented n-MOSFETs

Utilizing high pressure hydrogen annealing to realize forming free CBRAM

In this research, the forming-free CBRAM is realized by high pressure hydrogen annealing method (HPHA). With the structure of Cu/HfO2/TiN, the copper will be ionized by the hydrogen ion under the high pressure environment; meanwhile the copper ion will diffuse to the HfO2. Thus, the diffused copper ion can earlier form the precursor seed to generate the filament because of short migration distance. Besides, the characteristic of CBRAM is also improved, which can be explained by the experimental result and the proposed model.

Study of high-pressure hydrogen annealing effects on InGaZnO thin-film transistors

High-pressure hydrogen annealing (HPHA) treatment is an effective hydrogen doping method to improve electrical characteristics and stability of InGaZnO (IGZO) thin film transistors (TFTs). The HPHA effects on IGZO TFTs under various pressure conditions were investigated using analytical techniques. Drive current, field effect mobility, subthreshold swing, and bias stress stability of IGZO TFTs were significantly improved as the HPHA pressure was increased up to 20 atm. To analyze the performance enhancement, secondary ion mass spectroscopy, capacitance–voltage analysis, and x-ray photoelectron spectroscopy analysis techniques were performed. As a result, it was confirmed that doped hydrogen is combined with interface trap sites and oxygen vacancy related bulk defect sites, leading to improved subthreshold swing and bias stress stability. Furthermore, bulk trap passivation also contributes to high carrier density, thereby increasing driving current and field effect mobility. With increasing HPHA pressure condition, these effects of trap passivation and increase in the carrier density are more effective due to the heavily injected hydrogen.

Synergy effect of microwave annealing and high-pressure hydrogen annealing on Poly-Si thin-film transistor

Grain boundary (GB) is a significant factor that deteriorates the transfer characteristics of poly-Si thin-film transistors (TFTs). In this study, we utilized the synergistic effect of microwave annealing (MWA) and high-pressure hydrogen annealing (HPHA) to effectively reduce grain boundary trap (GBT) density, resulting in improved field-effect mobility (μ) and subthreshold swing (SS). To investigate the synergistic effect of MWA and HPHA, the transfer characteristics of rapid thermal annealing and forming gas annealing devices were compared and analyzed as control devices. Furthermore, the mechanism of SS and mobility enhancement can be quantitatively understood by lowering the GB barrier height. In addition, Raman spectroscopy proved that poly-Si crystallinity was improved during MWA. Our results showed that MWA and HPHA play a vital role in reducing GBT density and improving poly-Si TFT characteristics.

Hydrogen Barrier Properties of Atomic Layer Deposited Al2O3 with Different Oxidants for Ingazno Thin Film Transistor

Amorphous In-Ga-Zn-O (a-IGZO) semiconductors have been used as an active channel material in high mobility, flexible, and transparent thin film transistors (TFTs), but it is highly influenced by the external environment. Many factors could affect TFT performance, such as moisture, oxygen, and hydrogen, etc. Among them, hydrogen incorporation into the oxide semiconductor is unavoidable due to the high electronegativity of oxygen. Hydrogen incorporated into a-IGZO acts as a shallow donor by ionizing and bonding with oxygen to form hydroxyl groups, so that it makes the oxide TFT conductive and causes it not to show an on/off property.[1] Hydrogen can be incorporated through various processes, such as diffusion from ambient atmosphere, incorporation during the deposition of encapsulation layer, and diffusion from adjacent layer during post-annealing, etc. In particular, it has been observed that a large amount of hydrogen atoms produced by SiH4 plasma is incorporated into the a-IGZO layer, creating a shallow electron donor, when PE-CVD SiNx layer is deposited for encapsulation. [2] Thus, an appropriate hydrogen barrier is essential to prevent the inflow of hydrogen to the a-IGZO layer during the subsequent process. Therefore, a method of preventing hydrogen incorporation by chemical combination should also be performed. However, there is no systematic study to prevent hydrogen incorporation. The analysis of hydrogen atomic behavior in thin films with different properties have not been clearly examined so far, thus further studies for this are necessary. Techniques commonly used for the deposition of gas diffusion barrier deposition are sputtering, chemical vapor deposition (CVD), and atomic layer deposition (ALD). Among them, ALD is considered as the most promising method to produce the gas diffusion barrier for the encapsulation due to its special features, such as conformal deposition, defect-free, high-quality layer and excellent uniformity.[3], [4] Since the ALD process is based on sequential self-limiting surface reaction where growth occurs by depositing the material layer by layer, thin films with various properties can be obtained depending on the materials (precursor and reactant) used for deposition as well as the thermodynamic conditions.[5] In this study, Al2O3 was deposited on the a-IGZO TFT by atomic layer deposition (ALD) using trimethylaluminum (TMA) with water or O3, as the precursor and oxidant, respectively, at low temperature (about 60 °C). First, we fundamentally investigated the characteristics of Al2O3 according to the oxidant. The chemical composition of the Al2O3 was different depending on the oxidant used in the ALD process (XPS, FT-IR measurement). Based on this, we analyzed the effect of these characteristics on hydrogen barrier properties by using transfer curve (I-V measurement) and stress test of device. As a result, the device in which the Al2O3 was deposited exhibited excellent hydrogen barrier properties as compared with the bare device. There was no device degradation after the hydrogen treatment, which suggested the possibility of enhancing the stability by effectively blocking hydrogen in various fields and device reliability in mass production in the future. Reference [1] S. I. Oh, G. Choi, H. Hwang, W. Lu, and J. H. Jang, “Hydrogenated IGZO thin-film transistors using high-pressure hydrogen annealing,” IEEE Trans. Electron Devices, vol. 60, no. 8, pp. 2537–2541, 2013. [2] A. Sato et al., “Amorphous In-Ga-Zn-O thin-film transistor with coplanar homojunction structure,” Thin Solid Films, vol. 518, no. 4, pp. 1309–1313, 2009. [3] J. Meyer et al., “Al2O3/ZrO2Nanolaminates as ultrahigh gas-diffusion barriersa strategy for reliable encapsulation of organic electronics,” Adv. Mater., vol. 21, no. 18, pp. 1845–1849, 2009. [4] A. Dameron, S. Davidson, B. Burton, P. Carcia, R. McLean, and S. George, “Gas diffusion barriers on polymers using multilayers fabricated by Al2O3 and rapid SiO2 atomic layer deposition,” J. Phys. Chem. C, vol. 112, pp. 4573–4580, 2008. [5] S. M. George, A. W. Ott, and J. W. Klaus, “Surface Chemistry for Atomic Layer Growth,” J. Phys. Chem., vol. 100, no. 31, pp. 13121–13131, 1996. Figure 1

Improved Endurance of HfO2-Based Metal- Ferroelectric-Insulator-Silicon Structure by High-Pressure Hydrogen Annealing

We investigate the effects of high-pressure hydrogen annealing (HPHA) on W/ferroelectric Al:HfO2/interface layer (IL)/Si stacks. With HPHA, degradation in remnant polarization is observed in the pristine state due to ferroelectric domain pinning. However, after wake-up, a comparable remnant polarization is observed by domain de-pinning. In addition, HPHA improves the quality current and low interface trap density are maintained up to 107 cycles. As a result, the endurance improves up to 109 cycles and a stable retention is achieved up to 104 s at 85 °C. These results show that the HPHA can be a crucial process for ferroelectric HfO2-based transistor applications.

Unique reliability characteristics of fully depleted silicon-on-insulator tunneling FET

This study investigated the unique reliability characteristics of tunneling field effect transistors (TFETs) by comparing the effects of positive bias temperature instability (PBTI) and hot carrier injection (HCI) stresses. In case of hot carrier injection (HCI) stress, the interface trap generation near a p/n+ region was the primary degradation mechanism. However, strong recovery after a high-pressure hydrogen annealing and weak degradation at low temperature indicates that the degradation mechanism of TFET under the HCI stress is different from the high-energy carrier stress induced permanent defect generation mechanism observed in MOSFETs. Further study is necessary to identify the exact location and defect species causing TFET degradation; however, a significant difference is evident between the dominant reliability mechanism of TFET and MOSFET.

Contact Resistance Reduction of WS2 FETs Using High-Pressure Hydrogen Annealing

The transition metal dichalcogenides (TMDCs) have been extensively investigated for various applications such as logic, memory and optical devices, and sensors. The pressing challenge in the research of TMDCs is the electrical performance limited by the high contact resistance. We report more than 5000 times reduction in the contact resistance of WS2 field-effect transistor (FET) with Ti contact (81 M $\Omega ~\mu$ m to 14.6 k $\Omega ~\mu$ m) by high-pressure hydrogen annealing. Schottky barrier height reduction appears to play a major role in the reduction of the contact resistance. This process can be used to reduce the contact resistance even further by combining with a doping technique for TMDCs and a contact metal optimization for TMDC FETs.

Effects of High-Pressure Hydrogen Annealing (HPHA) on Reliability Characteristics of RRAM.

Reliability characteristics (retention and endurance) of RRAM are critical for its practical realization and need to be improved. In this work, we confirmed the trade-off between retention and endurance by using various top electrode thickness conditions. The trade-off between retention and endurance characteristics was mainly due to the different amount of oxygen in scavenging layer (Ta) and the amount of oxygen vacancy in switching layer (HfO2). The amount of the oxygen in scavenging layer (Ta) and the amount of the oxygen vacancy in switching layer (HfO2) will be increased with the increase of Ta thickness. Therefore, the thicker Ta cells have worse retention because the large amount of oxygen in scavenging layer (Ta) can diffuse back into switching layer (HfO2) and recombine with oxygen vacancies in the filament. However, it has longer endurance because the large amount of oxygen vacancy in switching layer (HfO2) can be a source of the filament. Hence, there exists a trade-off relation between retention and endurance under the various Ta thickness conditions. To improve both retention and endurance characteristics, we proposed a new method by using high-pressure hydrogen annealing (HPHA). The thin Ta cells have longer retention and worse endurance because it has small amount of both oxygen in scavenging layer (Ta) and oxygen vacancy in switching layer (HfO2). Therefore, to generate more oxygen vacancies in switching layer (HfO2) maintaining small amount of oxygen in scavenging layer (Ta), we treated the samples by HPHA before Ta deposition. Finally, we obtained both improved retention and endurance characteristics in HfO2 based RRAM devices after high-pressure hydrogen annealing treatment.

Comparative Studies of Long-Term Ambiance and Electrical Stress Stability of IGZO Thin-Film Transistors Annealed Under Hydrogen and Nitrogen Ambiance

The stability of hydrogenated indium–gallium–zinc-oxide (IGZO) thin-film transistors (TFTs) was investigated. Hydrogenation of the IGZO TFTs was carried out by high-pressure hydrogen annealing. The IGZO TFTs annealed under nitrogen (N2) ambiance were also fabricated for the comparative studies. The devices were kept in the air ambiance, and their performance was periodically measured to investigate their long-term stability. The long-term stability of the hydrogenated TFTs was better than that of the N2-annealed TFTs. Electrical bias stress was applied to both the types of the IGZO TFTs to study the electrical robustness of the devices. Under positive gate-bias stress, the optimized hydrogenated IGZO TFTs exhibited better reliability than those annealed in N2 ambiance in terms of threshold voltage ( $V_{{\mathrm{th}}}$ ) and saturation mobility ( $\mu _{{\mathrm{sat}}}$ ).

Proton Inserted SiO2 Dielectrics for Nonvolatile Memory-Thin Film Transistor

We demonstrated the nonvolatile memory functionality of both nano-crystalline silicon (nc-Si) and amorphous indium gallium zinc oxide (a-IGZO) field effect transistors (FETs) using mobile protons that are generated by very short time (within 5 minutes) hydrogen neutral beam (H-NB) treatment at room temperature (25 °C). Some researches try to hydrogen insertion process via long time (40 minutes) high-pressure hydrogen annealing (HPHA) at high temperature (400 °C) that also need several steps such as poly silicon deposition, HPHA process, and poly silicon etching process. However our hydrogen insertion process does not need any other additional process but only H-NB process during normal thin film transistor fabrication. Also the whole memory fabrication process kept under 50 °C (except SiO2 deposition process; 300 °C). These NVM-TFT(nc-Si and a-IGZO) and devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We also investigated neutral beam energy effect on non-volatile memory functionality with IGZO NVM-TFTs. The hysteresis widths of the IGZO NVM-TFTs exhibited strong linear dependency on the H-NB treatment energy. We expected this result from the energy dependent hydrogen surface density profile. The sandwiched hydrogen between insulators becomes mobile proton without annealing process. This H-NB dependent mobile proton density variation is meaningful because until now the only way to increase proton density was increasing ambient temperature or annealing time. The hydrogen neutral beam process between insulators to generate mobile proton is easily controlled by reflector bias. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a probability of next generation flexible memorable electronics such as low power consumption flexible display panel. Figure 1

Nonvolatile Memory Device Using Mobile Protons via Insertion Hydrogen Neutral Beam Treatment Process between SiO2 Deposition Processes at Room Temperature

We demonstrated the nonvolatile memory functionality of nano-crystalline silicon (nc-Si) field effect transistors (FETs) using mobile protons that are generated by very short time (within 2 minutes) hydrogen neutral beam (H-NB) treatment at room temperature (25 °C). Some researches try to hydrogen insertion process via long time (40 minutes) high-pressure hydrogen annealing (HPHA) at high temperature (400 °C) that also need several steps such as poly silicon deposition, HPHA process, and poly silicon etching process. However our hydrogen insertion process does not need any other additional process but only H-NB process during normal thin film transistor fabrication. Also the whole memory fabrication process kept under 50 °C (except SiO2deposition process; 300 °C). These nc-Si devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We think that the memory characteristics are attributed to the movement of protons between the Si(gate)/SiO2(gate insulator) interface and the SiO2/nc-Si thin film (active layer) interface by the applied gate electric field. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a modified CMOS platform for FET memory devices using nanomaterials, and probability of next generation flexible memorable electronics.

Effects of High-Pressure Hydrogen Annealing on the Formation of Conducting Filaments in Filament-Type Resistive Random-Access Memory

Accurate control of formation of conducting filaments is one of the most important challenges to solve in order to achieve improved switching characteristics in resistive random-access memory (ReRAM). In this regard, high-pressure hydrogen annealing (HPHA) can be an effective method for accurate control because it can induce in the ReRAM the formation of oxygen vacancies and OH– bonds, the main factors that influence conducting filament formation. Among the various switching processes, the forming process, which represents the first formation of a conducting filament, was investigated to clarify the effects of HPHA on the formation of conducting filaments. HPHA-treated samples were found to exhibit more accurately controlled resistance of the conducting filament, owing to accurate control of the forming process, compared with samples not treated by HPHA.

Hydrogenated IGZO Thin-Film Transistors Using High-Pressure Hydrogen Annealing

Hydrogenation of thin-film indium-gallium-zincoxide (IGZO) is carried out by applying a high-pressure hydrogen annealing (HPHA) process under 5-atm pressure at different temperatures of 260°C, 270°C, and 280°C. The HPHA effectively increases the carrier concentration and the Hall mobility up to ~ 1019 cm-3 and ~ 6.4 cm2/Vs, respectively. The HPHA-IGZO films exhibit smoother surfaces as compared with the as-grown films. The HPHA performs at a temperature of 260 °C that greatly enhances the electrical characteristics of IGZO TFTs, leading to a saturation field effect mobility of 7.4 cm2/Vs, a subthreshold slope of 0.37 V/decade, a threshold voltage of 2.2 V, and an ION/IOFF of 2.0×106.

Defect engineering: reduction effect of hydrogen atom impurities in HfO2-based resistive-switching memory devices

In this study, we propose a new and effective methodology for improving the resistive-switching performance of memory devices by high-pressure hydrogen annealing under ambient conditions. The reduction effect results in the uniform creation of oxygen vacancies that in turn enable forming-free operation and afford uniform switching characteristics. In addition, H+ and mobile hydroxyl (OH−) ions are generated, and these induce fast switching operation due to the higher mobility compared to oxygen ions. Defect engineering, specifically, the introduction of hydrogen atom impurities, improves the device performance for metal–oxide-based resistive-switching random access memory devices.

Nonvolatile Memory Functionality of ZnO Nanowire Transistors Controlled by Mobile Protons

We demonstrated the nonvolatile memory functionality of ZnO nanowire field effect transistors (FETs) using mobile protons that are generated by high-pressure hydrogen annealing (HPHA) at relatively low temperature (400 °C). These ZnO nanowire devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We show that the memory characteristics are attributed to the movement of protons between the Si/SiO(2) interface and the SiO(2)/ZnO nanowire interface by the applied gate electric field. The memory mechanism is explained in terms of the tuning of interface properties, such as effective electric field, surface charge density, and surface barrier potential due to the movement of protons in the SiO(2) layer, consistent with the UV photoresponse characteristics of nanowire memory devices. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a modified CMOS platform for FET memory devices using nanomaterials.

Improvement of interface quality by post-annealing on silicon nanowire MOSFET devices with multi-wire channels

We have investigated the passivation effects of high-pressure hydrogen annealing (HPHA) on silicon nanowire (Si NW) metal oxide semiconductor field effect transistors (MOSFETs) with multi-wire channels. Compared to the conventional forming gas annealing (FGA) process, the results show that HPHA can significantly improve device performance parameters such as threshold voltage, subthreshold slope, mobility, and ION/IOFF ratio. This enhancement is attributed to the effective passivation of the interface traps between the SiO2 and the Si NW channel. Therefore, HPHA can be a promising process for the implementation of the Si NW MOSFET.

Effect of passivation process in upgraded metallurgical grade (UMG)-silicon solar cells

We have investigated the effect of high-pressure pure hydrogen annealing (HPHA) for upgraded metallurgical grade (UMG)-silicon solar cell in order to obtain cost-effective high-efficiency cell using post-metallization anneal at a relatively low temperature. We have observed that high-pressure pure hydrogen annealing effectively passivated the defects and improved the minority carrier lifetime, series resistance and conversion efficiency. It can be attributed to significantly improved hydrogenation in high-pressure pure hydrogen process. This improvement can be explained by the enhanced hydrogenation of silicon solar cell with antireflection layer due to hydrogen re-incorporation. The results of this experiment represent a promising guideline for improving the high-efficiency solar cells by introducing an easy and low cost process of post-hydrogenation in optimized condition.

Improved Electrical Characteristics of Fully Depleted Ultrathin SOI MOSFETs Annealed in High-Pressure Hydrogen Ambient

We have investigated the effect of high-pressure hydrogen annealing (HPHA) on fully depleted silicon-on-insulator (SOI) metal-oxide semiconductor field-effect transistors (MOSFETs). The relatively high interface state density of back interface induces significant performance degradation due to the strong interface coupling effect between the front and back interface. To reduce this problem, we performed HPHA in 100% hydrogen ambient at 10 atm. We found that HPHA can significantly reduce the interface state density of both front and back interfaces, which in turn improves electron mobility. Considering the simple process condition and improved electrical characteristics, HPHA is a promising process technology for SOI MOSFETs.

HPHA Effect on Reversible Resistive Switching of Pt∕Nb-Doped SrTiO[sub 3] Schottky Junction for Nonvolatile Memory Application

We investigated the effect of high-pressure hydrogen annealing (HPHA) on a Pt/Nb-doped SrTiO 3 Schottky junction for nonvolatile memory applications. Hysteretic current-voltage (I-V) characteristic curves reveal that the HPHA-treated Schottky junction interface has a higher resistance ratio than the control sample in dc bias sweep. The HPHA sample also exhibits switching behavior by pulsed voltage stress with excellent electrical characteristics including voltage pulse duration as short as 1 μs, endurance cycles of up to 10 6 times, and retention time as long as 10 5 s. These indicate that HPHA improved resistance switching characteristics of the Schottky junction.