Unipolar Resistive Random Access Memory Research Articles

Improving Unipolar Resistive Switching Uniformity with Cone-Shaped Conducting Filaments and Its Logic-In-Memory Application.

Resistive random access memory (RRAM) with inherent logic-in-memory capability exhibits great potential to construct beyond von-Neumann computers. Particularly, unipolar RRAM is more promising because its single polarity operation enables large-scale crossbar logic-in-memory circuits with the highest integration density and simpler peripheral control circuits. However, unipolar RRAM usually exhibits poor switching uniformity because of random activation of conducting filaments and consequently cannot meet the strict uniformity requirement for logic-in-memory application. In this contribution, a new methodology that constructs cone-shaped conducting filaments by using chemically a active metal cathode is proposed to improve unipolar switching uniformity. Such a peculiar metal cathode will react spontaneously with the oxide switching layer to form an interfacial layer, which together with the metal cathode itself can act as a load resistor to prevent the overgrowth of conducting filaments and thus make them more cone-like. In this way, the rupture of conducting filaments can be strictly limited to the tip region, making their residual parts favorable locations for subsequent filament growth and thus suppressing their random regeneration. As such, a novel "one switch + one unipolar RRAM cell" hybrid structure is capable to realize all 16 Boolean logic functions for large-scale logic-in-memory circuits.

Improved Off-Current and Modeling in Sub-430 °C Si p-i-n Selector for Unipolar Resistive Random Access Memory

Despite the excellent performance of silicon-based selector devices, high epitaxy temperature ( $\text{T}_{\mathrm {epi}}\,>\,700~^{\circ }\text{C}$ ) is the key constraint for Si selector technology compatibility with back-end-of-the-line (BEOL) process. Recently, we have demonstrated the high performance sub-430 °C epitaxial Si p-i-n selector. In this letter, we identify a two-step mechanism that affects the off-current ( $I_{\mathrm{\scriptscriptstyle OFF}}$ ) performance of low temperature epitaxial Si p-i-n diodes using molecular beam epitaxy (MBE). First, the $\text{T}_{\mathrm {epi}}$ dependent i-region encroachment by surface dopant segregation shows excellent agreement with the surface diffusion model and demonstrates its validity down to 400 °C. Second, the trap assisted tunneling model is used to evaluate the impact of the modified i-region thickness (due to surface dopant segregation) on $I_{\mathrm{\scriptscriptstyle OFF}}$ . Improved ideality factor ( $2\times $ ) and $I_{\mathrm{\scriptscriptstyle OFF}}$ performance ( $10^{2}\times $ ) of sub-430 °C p-i-n diode is related to contamination control—a critical challenge in BEOL processing. Based on the experimentally validated model, we present the $I_{\mathrm{\scriptscriptstyle OFF}}$ dependence on the i-region thickness. We show that i-region thickness of 50 nm produces sufficiently low leakage, while higher i-region produces marginal $I_{\mathrm{\scriptscriptstyle OFF}}$ improvement. Thus, the low temperature epitaxial Si p-i-n junction technology is a promising step toward BEOL compatible Si selector technology.

Enhanced endurance reliability and low current operation for AlOx/HfOx based unipolar RRAM with Ni electrode

A 1-nm-thick AlOx layer is adopted to successfully eliminate soft-errors and reduce the operation current in HfOx based unipolar resistive random access memory (RRAM) with Ni as top electrode. Ni/HfOx/TiN RRAMs with one transistor–one resistor configuration during repetitive programming/erasing suffer serious soft-errors. The AlOx layer can share the applied voltage and suppress the soft-errors in the AlOx/HfOx based RRAM in high resistance state. The AlOx layer also modifies the conductive filaments in the devices with the low resistance to avoid the unexpected resistive switching. The forming/SET voltage, the high resistance state, and the on/off ratio in the Ni/AlOx RRAMs are larger than those of Ni ones. In particular, the soft-errors in the devices with ramped voltage verification are eliminated. The intermediate AlOx film is also beneficial for the reduced operation current of the device, which is as low as 10μA with a pulse width of 40ns.

Dual random circuit breaker network model with equivalent thermal circuit network

A SPICE-based dual random circuit breaker (RCB) network model with an equivalent thermal circuit network has been proposed in order to emulate resistance switching (RS) of unipolar resistive random access memory (RRAM). The dual RCB network model consists of the electrical RCB network model for the forming and set operations and the equivalent thermal circuit network model for the reset operation. In addition, the proposed model can explain the effects of heat dissipation on the memory and threshold RS with the variation in electrode thickness.

Cycle-to-Cycle Intrinsic RESET Statistics in ${\rm HfO}_{2}$-Based Unipolar RRAM Devices

The statistics of the RESET voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> ) and the RESET current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> ) of Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt resistive random access memory (RRAM) devices operated under unipolar mode are analyzed. The experimental results show that both the distributions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> are strongly influenced by the distribution of initial resistance in the ON state ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ), which is related to the size of the conductive filament (CF) before RESET. By screening the statistical data into different resistance ranges, both the distributions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> are shown to be compatible with a Weibull model. Contrary to previous reports for NiO-based RRAM, the Weibull slopes of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> are demonstrated to be independent of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . This is an indication that the RESET point, defined in this letter as the point of maximum current, corresponds to the initial phase of CF dissolution. On the other hand, given that the scale factor of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> distribution ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET63%</sub> ) is roughly independent of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> , the scale factor of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET</sub> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RESET63%</sub> ) is inversely proportional to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> . This is analogous to what was found in NiO-based RRAM and it is consistent with the thermal dissolution model of RESET. Our results highlight the intrinsic link between the SET and RESET statistics and the need for controlling the variation of ON-state resistance to reduce the variability of the RESET voltage and current.

Dimensional Effect of Non-Polar Resistive Random Access Memory (RRAM) for Low-Power Memory Application

The relationships between the resistive cell dimension and the related analytical parameters such as the forming voltage, set voltage, and reset current were investigated to implement high-density and low-power unipolar RRAM. It was shown that the formation process in unipolar switching is strongly related to the cell dimension in the sub-nm region, not only in terms of its vertical thickness but also of its horizontal length, using the numerical simulation method. With the optimal cell size having sufficient initial resistance and a low forming voltage, the achievement of the greatest feasibility of the high-density low-power RRAM will be further accelerated. A numerical simulation was performed using a random circuit breaker (RCB) simulation model to investigate the optimal resistive switching condition. The on/off resistance ratio increases as the cell area decreases at the sub-nm level, and these phenomena are explained in terms of the relatively large set resistance change in a very small area due to the conductive defect (CD) amount effect in the RCB network model.

Novel Protruded-Shape Unipolar Resistive Random Access Memory Structure for Improving Switching Uniformity through Excellent Conductive Filament Controllability

Resistive random access memory (RRAM) with a new structure which can effectively control switching area and electric field is proposed. It has been verified that the decrease in area of resistive material with the new structure increases electric field of switching area, and that such increased electric field makes initial forming at unipolar switching rather easier, resulting in effective decrease in forming voltage. Also, as the area in switching area is effectively reduced, decrease in reset current and set voltage in a limited area has also been verified. Excellent resistive switching characteristics are possible by decrease of conductive filament (CF) area in our structure. Random circuit breaker (RCB) simulation model which can effectively explain percolation switching similar to unipolar switching verifies such structural effect.

Novel Protruded-Shape Unipolar Resistive Random Access Memory Structure for Improving Switching Uniformity through Excellent Conductive Filament Controllability

Novel Protruded-Shape Unipolar Resistive Random Access Memory Structure for Improving Switching Uniformity through Excellent Conductive Filament Controllability

Reset Current Reduction with Excellent Filament Controllability by Using Area Minimized and Field Enhanced Unipolar Resistive Random Access Memory Structure

We firstly propose a novel resistive random access memory (RRAM) cell structure, which makes it possible to minimize the switching area and to maximize the electrical field where resistive switching occurs, resulting in the improvement of resistive switching characteristics. With excellent structural advantages, resistive switching characteristics such as reset current and set voltage fluctuation are improved through the enhancement of conductive filament (CF) controllability. A simple fabrication process is delivered and the device performance from the viewpoints of the forming voltage, set voltage, and reset current is investigated. Conducting defect effects are also investigated in comparison with the conventional RRAM cell structure. Numerical simulation is performed using a random circuit breaker (RCB) model to confirm the proposed structure.

Areal and Structural Effects on Oxide-Based Resistive Random Access Memory Cell for Improving Resistive Switching Characteristics

A new technical improvement in understanding the resistive switching characteristics of unipolar resistive random access memory (RRAM) is investigated. It is possible to minimize reset current (IRESET), set voltage variation, and forming voltage (VFORMING), which results in a wide sensing margin and high density applications by using a conducting filament (CF) minimized structure up to a 10 nm technology node. Its structural advantages enable IRESET to be tuned with excellent manufacturability. Numerical simulation is also performed using a random circuit breaker (RCB) model, showing that the proposed structure elucidates the resistive switching improvement.

Reset Current Reduction with Excellent Filament Controllability by Using Area Minimized and Field Enhanced Unipolar Resistive Random Access Memory Structure

Reset Current Reduction with Excellent Filament Controllability by Using Area Minimized and Field Enhanced Unipolar Resistive Random Access Memory Structure

A unified model for unipolar resistive random access memory

A unified model for resistive random access memory has been proposed for the accurate prediction of forming, reset, and set operations. Unlike conventional random circuit breaker network model, the unified model can simulate realistic cell structures with higher accuracy.

Ni Electrode Unipolar Resistive RAM Performance Enhancement by $\hbox{AlO}_{y}$ Incorporation Into $\hbox{HfO}_{x}$ Switching Dielectrics

In this letter, a high-performance unipolar resistive random access memory with Ni electrode/ HfOx/AlOy/p+-Si substrate structure is reported. Compared with Ni/HfOx/p+ -Si devices, a significant improvement in terms of switching parameters such as set/reset voltages, on/off resistance ratio, and resistance distribution is successfully demonstrated. It is believed that the stabilization of the conductive filament generation inside the switching HfOx film due to the AlOy incorporation plays a key role for the improved performance.

Resistive Random Access Memory (ReRAM) Based on Metal Oxides

In this paper, we review the recent progress in the resistive random access memory (ReRAM) technology, one of the most promising emerging nonvolatile memories, in which both electronic and electrochemical effects play important roles in the nonvolatile functionalities. First, we provide a brief historical overview of the research in this field. We also provide a technological overview and the epoch-making achievements, followed by an account of the current understanding of both bipolar and unipolar ReRAM operations. Finally, we summarize the challenges facing the ReRAM technology as it moves toward the beyond-2X-nm generation of nonvolatile memories and the so-called beyond complementary metal-oxide-semiconductor (CMOS) device.