Tsung-Ming Tsai

Physical and chemical mechanisms in oxide-based resistance random access memory

In this review, we provide an overview of our work in resistive switching mechanisms on oxide-based resistance random access memory (RRAM) devices. Based on the investigation of physical and chemical mechanisms, we focus on its materials, device structures, and treatment methods so as to provide an in-depth perspective of state-of-the-art oxide-based RRAM. The critical voltage and constant reaction energy properties were found, which can be used to prospectively modulate voltage and operation time to control RRAM device working performance and forecast material composition. The quantized switching phenomena in RRAM devices were demonstrated at ultra-cryogenic temperature (4K), which is attributed to the atomic-level reaction in metallic filament. In the aspect of chemical mechanisms, we use the Coulomb Faraday theorem to investigate the chemical reaction equations of RRAM for the first time. We can clearly observe that the first-order reaction series is the basis for chemical reaction during reset process in the study. Furthermore, the activation energy of chemical reactions can be extracted by changing temperature during the reset process, from which the oxygen ion reaction process can be found in the RRAM device. As for its materials, silicon oxide is compatible to semiconductor fabrication lines. It is especially promising for the silicon oxide-doped metal technology to be introduced into the industry. Based on that, double-ended graphene oxide-doped silicon oxide based via-structure RRAM with filament self-aligning formation, and self-current limiting operation ability is demonstrated. The outstanding device characteristics are attributed to the oxidation and reduction of graphene oxide flakes formed during the sputter process. Besides, we have also adopted a new concept of supercritical CO2 fluid treatment to efficiently reduce the operation current of RRAM devices for portable electronic applications.

Atomic-level quantized reaction of HfOx memristor

In this study, we have observed dynamic switching behaviors in a memristive device. There are only a few atoms in the resistive switching reaction which enables the high-speed resistive switching characteristics, which was analyzed dynamically by real-time analyzing tools. From fundamental conductance considerations, the resistance of the conductive path in HfOx memristor is found to be due to barriers which are atomically incremented during the RESET process. Simultaneously, we have demonstrated the quantized switching phenomena at ultra-cryogenic temperature (4 K), which are attributed to the atomic-level reaction in metallic filament.

Characteristics and Mechanisms of Silicon-Oxide-Based Resistance Random Access Memory

Traditionally, a large number of silicon oxide materials are extensively used as various dielectrics for semiconductor industries. In general, silicon oxide cannot be used as resistance random access memory (RRAM) due to its insulating electrical properties. In this letter, we have successfully produced resistive switching and forming-free behaviors by zinc doped into silicon oxide. The current-voltage fitting data show that current transport mechanism is governed by Poole-Frenkel behavior in high-resistance state and Ohms law in low-resistance state, consisting with filament theory. Additionally, good endurance and retention reliabilities are exhibited in the zinc-doped silicon oxide RRAM.

Bipolar Resistive RAM Characteristics Induced by Nickel Incorporated Into Silicon Oxide Dielectrics for IC Applications

In this letter, we successfully produced resistive switching behaviors by nickel doped into silicon oxide at room temperature. The nickel element was doped into silicon oxide, which is a useful dielectric material in integrated circuit (IC) industries by cosputtering technology. Based on the proposed method, satisfactory reliability of the resistance switching device can be demonstrated by endurance and retention evaluation. We believe that the silicon oxide doped with nickel at room temperature is a promising method for resistive random access memory nonvolatile memory applications due to its compatibility with the IC processes.

Reducing operation current of Ni-doped silicon oxide resistance random access memory by supercritical CO2 fluid treatment

In the study, we reduced the operation current of resistance random access memory (RRAM) by supercritical CO2 (SCCO2) fluids treatment. The power consumption and joule heating degradation of RRAM device can be improved greatly by SCCO2 treatment. The defect of nickel-doped silicon oxide (Ni:SiOx) was passivated effectively by the supercritical fluid technology. The current conduction of high resistant state in post-treated Ni:SiOx film was transferred to Schottky emission from Frenkel-Pool due to the passivation effect. Additionally, we can demonstrate the passivation mechanism of SCCO2 for Ni:SiOx by material analyses of x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Eliminating dielectric degradation of low-k organosilicate glass by trimethylchlorosilane treatment

The interaction between low-k organosilicate glass (OSG) and photoresist removal is investigated. O2 plasma ashing and chemical wet stripper are commonly performed to remove photoresist (PR) in integrated circuit fabrication. However, O2 plasma or wet stripper will attack function groups and cause Si–OH group formation in OSG film during PR removal processing. The Si–OH groups often lead to moisture uptake and consequently dielectric degradation will occur in OSG film. Trimethylchlorosilane (TMCS) treatment can negate the damage in the OSG film after the PR removal process. In addition, chemical TMCS can react with Si–OH groups and reduces moisture uptake so that the dielectric characteristic of OSG can be maintained. Hence, TMCS treatment is a promising method for photoresist removal.

Low-power bipolar resistive switching TiN/HfO2/ITO memory with self-compliance current phenomenon

In this work, a TiN/HfO2/ITO memory device is fabricated, which shows stable bipolar resistive switching behavior, as well as excellent data retention and good endurance. Moreover, a very low SET voltage of 0.2 V is achieved with a self-compliance current effect. The result brings about an obvious reduction in SET power to 160 µW, which is crucial for future high-density resistive switching memories. On the basis of the conducting filament theory, a possible resistive mechanism is discussed to explain the low SET voltage and self-compliance current phenomenon.

Charge Quantity Influence on Resistance Switching Characteristic During Forming Process

In this letter, we presented that the charge quantity is the critical factor for forming process. Forming is a pivotal process in resistance random access memory to activate the resistance switching behavior. However, overforming would lead to device damage. In general, the overshoot current has been considered as a degradation reason during the forming process. In this letter, the quantity of charge through the switching layer has been proven as the key element in the formation of the conduction path. Ultrafast pulse forming can form a discontinuous conduction path to reduce the operation power.

Origin of Hopping Conduction in Sn-Doped Silicon Oxide RRAM With Supercritical

In this letter, we investigate the origin of hopping conduction in the low-resistance state (LRS) of a resistive random access memory device with supercritical CO2 fluid treatment. The dangling bonds of a tin-doped silicon oxide ( Sn:SiOx) thin film were cross linked by the hydration-dehydration reaction through supercritical fluid technology. The current conduction mechanism of the LRS in the posttreated Sn:SiOx thin film was transferred to hopping conduction from Ohmic conduction, owing to isolation of metal tin in the Sn:SiOx thin film by hydration-dehydration reaction. The phenomena can be verified by our proposed reaction model, which is speculated by the X-ray photoelectron spectroscopy analyses.

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The interaction between low dielectric constant (low-k) hybrid organic siloxane polymer (HOSP) and O 2 plasma ashing has been investigated. O 2 plasma ashing is commonly performed to remove the photoresist (PR) during integrated circuit fabrication. However, dielectric loss usually occurs in the HOSP films during the PR removal process. In order to eliminate dielectric loss originating from an O 2 plasma attack, hexamethyldisilazane (HMDS) treatment is proposed to repair the damage in the HOSP film. HMDS can react with Si-OH bonds and reduce moisture uptake. Moreover, the leakage current and the dielectric constant is decreased significantly when damaged HOSP film undergoes HMDS treatment. For this reason, HMDS treatment is a promising method to apply to the photoresist removal.