Disturb-Free MTPROM Cell With Source Node Voltage Clamping
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Solution Overview
Problem
In multiple-time programmable read-only memory (MTPROM) cells, charge trapping and de-trapping lead to threshold-voltage shifts due to oxygen vacancies in hafnium oxide, causing disturb issues that result in data corruption and degradation, especially in unprogrammed and previously programmed cells, which existing technologies fail to adequately address.
Innovation Solution
The implementation of a disturb control circuitry that isolates and clamps the internal source node voltage to a low level using a switched source line and diode configuration, preventing voltage fluctuations and data corruption by maintaining a voltage level around zero volts in unselected cells, thereby avoiding disturb during programming and read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a NOR-type array with common source-line network is used for programming and reading, then parallel write efficiency and read capability are improved, but voltage fluctuations cause disturb to unprogrammed cells and data corruption
Solution Approach 1:
The common source-line network is segmented into individual cell-level source nodes, each independently controllable. This allows selective programming of specific cells while isolating unprogrammed cells from voltage fluctuations, preventing disturb while maintaining parallel write capability.
Solution Approach 2:
Each cell is given independent control over its source node voltage, allowing local optimization during programming operations. Programmed cells receive high voltage for charge trapping while unprogrammed cells maintain stable low voltage, eliminating disturb effects.
2Adaptability or versatility
If charge trapping is used in hafnium oxide gate dielectric for bit storage, then multiple-time programmability is achieved, but oxygen vacancies cause threshold-voltage shifts and disturb
Solution Approach 1:
The circuit applies preliminary voltage clamping to prevent oxygen vacancy formation and charge trapping in unprogrammed cells before disturb can occur. By maintaining low voltage on unprogrammed cell source nodes during programming operations, the circuit preemptively prevents the formation of harmful oxygen vacancies.
Solution Approach 2:
An additional control transistor is introduced as an intermediary between the source line and each cell's source node. This intermediary device independently controls the voltage at each cell's source node, allowing precise control of charge trapping conditions and prevention of unwanted oxygen vacancy formation.
3Reliability
If twin cell approach with complement NMOS transistors is used, then sensitivity to Vt fluctuations is minimized, but complexity of cell structure increases
Solution Approach 1:
The disturb control circuitry is merged with the existing twin cell structure by sharing control transistors and integrating the voltage clamping function into the cell's existing transistor network. This reduces the net increase in complexity while maintaining the sensitivity benefits of the twin cell approach.
Solution Approach 2:
The additional control transistor serves multiple functions: it acts as a disturbance control element, a voltage clamp, and an isolation switch. This multi-functionality reduces the need for separate dedicated circuits, thereby limiting the increase in overall device 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 solution effectively prevents data corruption and degradation by isolating unprogrammed cells and maintaining stable voltage levels, ensuring reliable data storage and retrieval while minimizing the overhead of additional circuitry, thus enhancing the reliability and efficiency of MTPROM cells.
Implementation Method 1
the third device isolates and float the node such that a voltage level of a gate to source of the first device is clamped down by the fourth device to a voltage level around zero volts
Implementation Method 2
hafnium oxide has a propensity to form oxygen vacancies, where charge trapping produces threshold-voltage (Vt) shifts
Data Source
AI summary
Approaches for a memory including a cell array are provided. The memory includes a first device of the cell array which is connected to a bitline and a node and controlled by a word line, and a second device of the cell array which comprises a third device which is connected to a source line and the node and controlled by the word line and a fourth device which is connected between the word line and the node. In the memory, in response to another word line in the cell array being activated and the word line not being activated to keep the first device in an unprogrammed state, the third device isolates and floats the node such that a voltage level of a gate to source of the first device is clamped down by the fourth device to a voltage level around zero volts.