Crossbar RRAM Programming With Staged Transistor-Safe Voltages
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Solution Overview
Problem
Crossbar circuits face challenges in programming resistive random-access memory (RRAM) devices due to the constraints imposed by smaller transistors with reduced maximum allowed voltages, limiting the voltage supply to RRAM devices and hindering efficient scaling and operation.
Innovation Solution
A multi-step programming scheme is employed, incrementally raising word line, bit line, and select line voltages to desired levels without exceeding the maximum allowed voltage of the transistors, using current-mode digital-to-analog converters (IDACs) to control programming signals and ensure compliance with transistor limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the voltage supply to RRAM devices is increased to improve programming efficiency, then the programming speed and effectiveness are improved, but the transistor voltage constraint is violated causing device damage or malfunction
Solution Approach 1:
The voltage application process is segmented into multiple sequential steps. First, a first voltage is applied to the word line. Then, a second voltage is applied to the bit line. Finally, a third voltage is applied to the word line. This segmentation allows the total voltage across the RRAM device to reach the required programming level while ensuring that no single transistor exceeds its maximum voltage rating at any intermediate stage.
Solution Approach 2:
The multi-step voltage application sequence performs preliminary voltage buildup on the word line before applying the final voltage to the RRAM device. By pre-charging the word line to a first voltage level and then adding a second voltage level on the bit line, the system prepares the voltage conditions in advance to avoid sudden voltage spikes that would violate transistor constraints.
2Area of stationary object
If smaller transistors are used to reduce bit cell area, then the area efficiency is improved, but the maximum allowed voltage of transistors is reduced limiting RRAM programming capability
Solution Approach 1:
The voltage application is divided into three distinct steps with different voltage levels applied to different lines. This segmentation enables the use of lower-voltage transistors (enabling smaller transistor size and reduced bit cell area) while still achieving the total voltage required for effective RRAM programming by combining the voltage contributions from word line and bit line in sequence.
Solution Approach 2:
The solution moves from a single-voltage-dimension approach to a multi-dimensional voltage application scheme. Instead of applying one high voltage that would require large transistors, the system applies voltages in multiple dimensions (different lines at different times), effectively decoupling the transistor voltage rating from the total programming voltage requirement.
Data Source
AI summary
Methods for programming crossbar circuits are provided. The methods include initializing a word line voltage, a bit line voltage, and a select voltage applied to a cross-point device of the crossbar circuit. The methods further include raising the word line voltage without changing the bit line voltage. The bit line voltage may be raised without changing the word line voltage applied to the cross-point device. The word line voltage and the bit line voltage may be alternatively changed until they reach their respective desired values. In some embodiments, the methods further include setting the bit line voltage to a predetermined value and raising the word line voltage without changing the select voltage. The select voltage may then be raised without changing the word line voltage applied to the cross-point device. The word line voltage and the select voltage may be alternatively changed until they reach their respective desired values.