Nonvolatile Memory Pre-pulse Stabilization
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Solution Overview
Problem
The challenge in flash memory devices is the increase in leakage current due to the reduction in gate insulating film thickness, leading to data loss and difficulty in identifying data during read operations, especially with high dielectric materials that exhibit delay polarization, causing changes in the dielectric constant over time.
Innovation Solution
A nonvolatile semiconductor memory device and method that involves applying a pre-pulse signal to all memory cells in a memory string before reading data, with the pre-pulse having a lower voltage than the read signal, to stabilize the electric field and reduce channel current fluctuations, thereby maintaining data integrity and improving read operation stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the thickness of the gate insulating film is reduced to maintain controllability of the switching operation in downscaled memory cell transistors, then the controllability is improved, but the leakage current increases
Solution Approach 1:
The patent applies a composite insulating film structure consisting of a first insulating film (lower dielectric constant material such as SiO2 or Si3N4) and a second insulating film (higher dielectric constant material such as HfO2 or BaTiO3). This composite structure allows the use of thin film technology to maintain controllability while the lower-dielectric-constant first film reduces leakage current by providing a more stable barrier against charge loss.
2Object-generated harmful factors
If high dielectric materials are used for the insulating film to reduce equivalent oxide thickness and decrease leakage current, then the leakage current is reduced, but the dielectric constant changes with time due to delay polarization
Solution Approach 1:
The patent applies a pre-pulse signal to the memory cell before the actual read operation. This preliminary action allows the high dielectric material to undergo dielectric relaxation in advance, stabilizing its polarization state. By performing this preliminary conditioning, the subsequent read operation occurs when the dielectric constant has stabilized, eliminating time-dependent fluctuations during data identification.
Solution Approach 2:
The patent employs periodic pre-pulse signals applied at specific intervals before read operations. This periodic action maintains the dielectric material in a stable state by regularly resetting its polarization conditions, ensuring consistent dielectric constant values during subsequent read operations and preventing data identification errors.
3Object-generated harmful factors
If high dielectric materials with delay polarization are used, then the equivalent oxide thickness is reduced and leakage current decreases, but the channel current changes with time during read operation causing difficulty in identifying data
Solution Approach 1:
The patent applies a pre-pulse signal to the memory cell before the actual read operation. This preliminary action allows the high dielectric material to undergo dielectric relaxation in advance, stabilizing its polarization state. By performing this preliminary conditioning, the subsequent read operation occurs when the dielectric constant has stabilized, eliminating time-dependent fluctuations during data identification.
4Quantity of substance
If the memory cell transistor is downscaled to increase capacity, then the capacity is increased, but the insulating film thickness must be reduced which increases leakage current
Solution Approach 1:
The patent applies a composite insulating film structure consisting of a first insulating film (lower dielectric constant material such as SiO2 or Si3N4) and a second insulating film (higher dielectric constant material such as HfO2 or BaTiO3). This composite structure allows the use of thin film technology to maintain controllability while the lower-dielectric-constant first film reduces leakage current by providing a more stable barrier against charge loss.
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
The solution effectively reduces channel current fluctuations and stabilizes read operations, ensuring accurate data retrieval even with high dielectric materials, by pre-conditioning the memory cells with a pre-pulse signal, thus addressing the issue of data loss and identification challenges.
Implementation Method 1
The phenomenon that change with time occurs in the dielectric constant when applying an electric field to the insulating film is generally referred to as dielectric relaxation
Implementation Method 2
Polarization is generally categorized into instantaneous polarization and delay polarization
Data Source
AI summary
According to one embodiment, a nonvolatile semiconductor memory device includes a memory string including a plurality of memory cells and, a driving unit. In sequentially reading data stored in the memory cells by applying a first signal to the memory cells, a second signal is applied to a second cell. The driving unit applies a third signal to the gate electrodes of all the memory cells prior to the sequential reading. The third signal has a voltage smaller than the second signal and time duration equal to or more than that of a sum of time duration during which the first signal is applied to all the memory cells. In a period prior to the third signal application, the driving unit performs at least one of applying a fourth signal to the gate electrodes and matching a potential of the gate electrodes with that of the semiconductor layer.