Programmable Resistance Pull-Up Resistors for Compact SRAM Cells
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Solution Overview
Problem
Conventional SRAM cells require additional area and processing complexity due to polysilicon pull-up resistors, which impose spacing constraints and necessitate extra processing steps, such as doping and dual polysilicon processes.
Innovation Solution
The use of programmable resistance elements, specifically CBRAM type elements, as pull-up resistors in SRAM cells, which can be formed above the gate layer and require only the space of a contact, allowing for compact cell size and reduced processing complexity, and can be programmed between different resistance states using electric fields to induce oxidation-reduction reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If polysilicon pull-up resistors are used in conventional 4T SRAM cells, then the cell can provide compact size, but additional spacing constraints and processing complexity are imposed
Solution Approach 1:
The patent changes the resistance parameter of the pull-up element by using programmable resistance elements that can be set to high resistance states through voltage programming, eliminating the need for polysilicon resistors with fixed high resistance values that require additional doping processes
Solution Approach 2:
The patent extracts the pull-up resistor function from the polysilicon layer and implements it using programmable resistance elements formed in separate layers, removing the dependency on polysilicon doping processes and buried contacts
2Reliability
If polysilicon pull-up resistors are used, then high resistance can be achieved, but additional processing steps such as doping are required
Solution Approach 1:
The patent achieves high resistance values by programming the programmable resistance elements to high resistance states through voltage application, eliminating the need for thermal doping processes that are required to create high resistance polysilicon regions
Solution Approach 2:
The patent replaces the thermal doping process with an electrical programming process to set the resistance value, substituting a chemical/thermal manufacturing step with an electrical control mechanism
3Ease of manufacture
If dual polysilicon process is used, then pull-up resistors can be connected to substrate areas, but process complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts the pull-up resistor connection from the substrate level and implements it through programmable resistance elements that can be connected to substrate areas through simpler contact structures, eliminating the need for complex dual polysilicon processes and buried contacts
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
This solution provides high resistance pull-up resistors with low leakage currents, enabling improved signal noise margin and broad process stability, reducing power consumption and eliminating the need for well isolation structures, while allowing for nonvolatile storage capabilities.
Implementation Method 1
can be programmed between different resistance states using electric fields to induce oxidation-reduction reactions
Data Source
AI summary
An integrated circuit (IC) device can include static random access memory (SRAM) cells that each include a pair of latching devices, and first and second resistive elements disposed over the latching devices. The first resistive element can be conductively connected to a first data latching node by a first vertical connection. The second resistive element can be conductively connected to a second data latching node by a second vertical connection. Each resistive element can include at least one memory layer that is capable of being programmed between at least a high and lower resistance state by application of electric fields, the resistive elements having only the high resistance state.