Floating-Body Memory Cell Structure for RDF-Stable States
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Solution Overview
Problem
As memory cells are being scaled to smaller feature sizes, the variability in their characteristics increases due to Random Dopant Fluctuation (RDF), affecting the stability and reliability of semiconductor memory devices.
Innovation Solution
The semiconductor memory cell design incorporates a floating body region with specific doping concentration levels and a back-bias region that generates impact ionization in one state while preventing it in the other, maintaining stable states through bipolar transistor mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If memory cells are scaled to smaller feature sizes, then device density and integration are improved, but variability in cell characteristics increases due to Random Dopant Fluctuation
Solution Approach 1:
The patent changes the physical and chemical parameters of the transistor structure by implementing an electrically floating body configuration where the body region is isolated from the substrate by an insulating layer. This structural parameter change eliminates the need for dopant atoms in the body region, thereby removing the source of Random Dopant Fluctuation and its associated variability in threshold voltage and other cell characteristics, while enabling continued scaling for higher density.
2Ease of manufacture
If conventional doped transistors are used, then manufacturing processes are well-established, but Random Dopant Fluctuation causes instability in memory cell states
Solution Approach 1:
The patent extracts the dopant atoms from the transistor body region by isolating it with an insulating layer, creating an electrically floating body. This removal of dopants eliminates Random Dopant Fluctuation and its harmful effects on memory cell state stability, while the insulating layer can be integrated into existing manufacturing processes using standard isolation techniques.
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 design stabilizes memory cell states by ensuring consistent charge retention and reduced variability, enhancing the reliability of semiconductor memory devices.
Implementation Method 1
a back-bias region configured to generate impact ionization when the memory cell is in one of the first and second states
Data Source
AI summary
A semiconductor memory cell includes a floating body region configured to be charged to a level indicative of a state of the memory cell selected from at least first and second states. A first region of the memory cell is in electrical contact with the floating body region. A second region of the memory cell is spaced apart from the first region and is also in electrical contact with the floating body region. A gate is positioned between the first and second regions. A back-bias region is configured to generate impact ionization when the memory cell is in one of the first and second states, and the back-bias region is configured so as not to generate impact ionization when the memory cell is in the other of the first and second states.