RRAM Cell with Bidirectional Two-State Resistor for Crosstalk Suppression
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Solution Overview
Problem
Bipolar Resistive Random Access Memories (RRAMs) face challenges with reading crosstalk in crossbar arrays due to symmetric I-V characteristics, leading to misread states and reduced storage density, as normal unidirectional rectifying diodes cannot supply sufficient current for erasing operations.
Innovation Solution
A RRAM cell comprising a two-state resistor and a resistive switching memory cell connected in series, where the two-state resistor exhibits bidirectional rectifying characteristics, allowing for large operation currents under both positive and negative voltages, thereby reducing leakage paths and suppressing reading crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If normal unidirectional rectifying diodes are used in bipolar RRAM cells, then reading crosstalk is suppressed, but erasing operation current is insufficient
Solution Approach 1:
The patent employs an n-p-n junction transistor instead of a simple diode, utilizing the asymmetric current-voltage characteristics of bipolar transistors. The transistor provides strong rectifying action in the forward active mode for reading operations while enabling sufficient current drive in both forward and reverse directions for programming and erasing operations, thus resolving the contradiction between crosstalk suppression and erasing current capability.
Solution Approach 2:
The patent changes the electrical parameters of the selector device by using a bipolar transistor with configurable base-emitter and base-collector junctions. By controlling the doping concentrations and junction characteristics, the device achieves different resistance states that enable both effective crosstalk suppression during reading and sufficient current delivery during erasing operations.
2Reliability
If transistors are used as selector devices in 1T1R configuration, then reading crosstalk is suppressed, but cell area increases
Solution Approach 1:
The patent merges the selector transistor with the RRAM cell structure in a 1T1R configuration where the transistor shares the bit line and word line connections with the resistive memory element. This integration allows the transistor to serve dual purposes as both selector and access device, achieving crosstalk suppression while minimizing the additional area overhead compared to separate selector and memory cell structures.
3Quantity of substance
If RRAM cells are arranged in crossbar array, then storage density is improved, but reading crosstalk increases due to symmetric I-V characteristics
Solution Approach 1:
The patent introduces asymmetric n-p-n junction transistors at each crossbar intersection to provide non-reciprocal current conduction. The transistor's inherent asymmetry in forward and reverse bias characteristics enables selective activation of memory cells during reading operations, preventing current leakage through non-selected cells and eliminating reading crosstalk while preserving the high-density crossbar array architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The bidirectional rectifying two-state resistor effectively serves as a selector device, reducing leakage paths and crosstalk in RRAM crossbar arrays, improving storage density by enabling accurate reading and writing operations.
Implementation Method 1
The two-state resistor may comprise a lower conductive electrode, a two-state resistor functionality layer, and a middle conductive electrode. The two-state resistor functionality layer may comprise an n-p-n junction or a p-n-p junction consisted of any one or more of doped Si, Ge, GaAs, InP, and SiGe.
Data Source
AI summary
A Resistive Random Access Memory (RRAM) cell and a memory are disclosed. In one embodiment, the RRAM cell comprises a two-state resistor and a resistive switching memory cell connected in series. The two-state resistor can supply relatively large currents under both positive and negative voltage polarities. As a result, it is possible to reduce leakage paths in a crossbar array of memory cells, and thus to suppress reading crosstalk.