Floating Body BiCMOS Flash Cell Voltage Reduction
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Solution Overview
Problem
The integration of non-volatile memory cells into BiCMOS fabrication processes is challenging due to the need for additional masks and process steps, which increases costs and reduces yields, as BiCMOS feature sizes are larger and device performance is slower compared to CMOS and bipolar techniques.
Innovation Solution
A floating gate-type non-volatile memory device is created using standard BiCMOS process flows by combining bipolar P-type base and 'ZN+' emitter diffusions with CMOS FET N-well diffusion and polysilicon gate structures, isolating the P-body from the P-substrate without requiring a triple-well arrangement, thus reducing the voltage needed for Fowler-Nordheim tunneling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If triple-well process is used to isolate P-body, then voltage requirement for Fowler-Nordheim tunneling is reduced, but manufacturing complexity and cost increase due to additional masks and process steps
Solution Approach 1:
The patent merges the P-body isolation function with the N-well structure already present in standard BiCMOS processes. By forming the P-body within the N-well region and using the N-well as the isolation mechanism, the patent eliminates the need for separate triple-well processing while achieving the same voltage reduction effect for Fowler-Nordheim tunneling.
Solution Approach 2:
The N-well structure serves dual purposes: it acts as both the substrate for NMOS devices and as the isolation structure for the P-body in flash memory cells. This multi-functionality allows standard BiCMOS processes to produce isolated P-bodies without requiring additional specialized processing steps.
2Adaptability or versatility
If non-conforming circuit structures are added to BiCMOS process flow, then non-volatile memory functionality is achieved, but productivity decreases due to increased processing time and cost
Solution Approach 1:
The patent designs the flash memory cell to use the same N-well and P-base structures that are fundamental to BiCMOS technology. By making the memory cell conform to existing BiCMOS process capabilities rather than requiring new process steps, the patent maintains high productivity while achieving non-volatile memory functionality.
Solution Approach 2:
The standard BiCMOS process structures (N-well, P-base, polysilicon gate) serve the dual purpose of creating both bipolar transistors and flash memory cells. The existing process flow automatically provides the necessary structures for memory functionality without requiring additional self-service processing steps.
3Ease of manufacture
If P-body is not isolated, then manufacturing is simpler, but voltage pumping requirement increases to achieve minimum electric field for Fowler-Nordheim tunneling
Solution Approach 1:
The patent combines the P-body formation with the N-well structure creation in a single process step. The P-body is formed within the N-well region using the same diffusion or implantation step that creates the N-well, thereby achieving isolation without additional manufacturing complexity.
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 approach allows for the production of non-volatile memory cells with reduced voltage requirements, minimizing the need for additional masks and process steps, thereby maintaining cost-effectiveness and yield within standard BiCMOS flows.
Implementation Method 1
achieve a minimum electric field of 10 Mv/cm, which is the minimum required to produce the onset of Fowler-Nordheim tunneling
Data Source
AI summary
A BiCMOS integrated circuit (IC) includes a floating gate-type non-volatile memory (NVM) device that uses the polycrystalline silicon gate of a CMOS FET and the P-base and N-emitter diffusions of a bipolar transistor to provide an isolated P-type body and N-type source/drain diffusions. The P-body diffusion of the NVM device is isolated from a P-substrate by an N-well, thus facilitating the use of reduced positive and negative voltage levels to produce the onset of Fowler-Nordheim tunneling without the need for a triple-well structure. The polysilicon gate structure is formed on a suitable gate oxide over the P-body. The source/drain diffusions, which like the N-emitter diffusions of the bipolar transistor have no LDD, produce a reduced field drop across the gate oxide to allow Fowler-Nordheim tunneling from the source side.