Thin Oxide Memory Cell Using Hot Carrier Injection
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Solution Overview
Problem
Existing memory devices face challenges in achieving multiple programming cycles while maintaining cost-effectiveness, as they often require high programming voltages and thicker gate oxides, which increase manufacturing costs and reduce device reliability.
Innovation Solution
A memory cell with a thin gate oxide (less than 75 angstroms) using n-channel devices with two polysilicon layers, where programming is achieved by bipolar injection and channel hot hole programming at a voltage of 5 volts, allowing for one or multiple programming cycles without the need for high voltage support and reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a thicker gate oxide is used to enable multiple programming cycles, then the device can be programmed many times, but the manufacturing cost increases and device reliability decreases
Solution Approach 1:
The patent changes the programming mechanism from high-voltage direct tunneling through thick oxide to low-voltage hot carrier injection through thin oxide. By using n-channel devices with thin gate oxide (50-100nm) and applying hot carrier injection techniques, the device achieves multiple programming cycles without requiring thick oxide, thus maintaining reliability while enabling reprogrammability
Solution Approach 2:
The patent replaces the mechanical/stress-based thick oxide structure with an electrical field-based hot carrier injection mechanism. Instead of relying on physical oxide thickness to prevent charge leakage, the system uses controlled electrical fields to inject and trap carriers, achieving multiple cycles through electrical control rather than structural thickness
2Duration of action of stationary object
If a thicker gate oxide is used to ensure multiple programming cycles, then the device can be programmed many times, but the manufacturing cost increases
Solution Approach 1:
The patent changes the oxide thickness parameter from thick (required for multiple cycles in conventional designs) to thin (50-100nm), which is actually easier and cheaper to manufacture with standard CMOS processes. The thin oxide is compensated for by using hot carrier injection mechanisms that work effectively with thinner layers, reducing manufacturing complexity and cost
3Reliability
If high programming voltage is applied to program memory cells, then charge can be held by the memory cell, but the device requires high voltage support infrastructure
Solution Approach 1:
The patent replaces high-voltage direct programming with low-voltage hot carrier injection. By using standard CMOS voltages (3.3V or 5V) to generate hot carriers through channel heating, the system achieves effective programming without high voltage infrastructure. The hot carriers naturally tunnel into the floating gate at these lower voltages, eliminating the need for complex high voltage generation circuits
4Ease of manufacture
If n-channel devices with thin gate oxide are used, then manufacturing costs are reduced and high voltage support is eliminated, but the device must use bipolar injection and channel hot hole programming
Solution Approach 1:
The patent makes the n-channel device structure universal by demonstrating that hot carrier injection can achieve programming functionality traditionally associated with p-channel devices. The thin oxide n-channel structure performs multiple functions: it enables low-voltage operation, reduces manufacturing cost, and achieves programmability through hot carrier mechanisms, making it a versatile replacement for more complex high-voltage or p-channel designs
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 enables EPROM-like functionality with reduced manufacturing costs, achieving tens or hundreds of program/erase cycles while maintaining device reliability and eliminating the need for high voltage support, thus addressing the cost and efficiency challenges of existing memory devices.
Implementation Method 1
The programming voltage may be higher than a voltage used to a read content of the memory device, such that a charge may be held by a memory cell
Implementation Method 2
performing channel hot hole programming to program the memory cell
Implementation Method 3
performing bipolar injection to reset the memory cell of the programmable device
Data Source
Figure 1~2A
Figure 2B~2C
Figure 2D
AI summary
Methods and apparatus, including computer program products, for a one or multiple- times programmable memory device. A semiconductor may include an active region of a substrate, a thin oxide layer over a substrate, a first and second polysilicon layer, and a first and second metal layer. The first polysilicon layer may have a floating gate, the active region may be substantially perpendicular to the floating gate, and the second polysilicon layer may include a control gate. The first metal layer may include a bit line connected to a first n-diffused region, where the bit line is substantially perpendicular to the floating gate. The second metal layer may include a word line and source line. The word line may be connected to the control gate, and the source line may be connected to a second n-diffused region. The thin gate oxide may have a thickness between 65 and 75 angstroms.