Ferroelectric Capacitor Data Retention in Semiconductor Memory
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Solution Overview
Problem
In memory devices such as NOSRAM, the limited capacity of capacitors to retain electric charge leads to decreased data reading accuracy and short-term data retention.
Innovation Solution
A semiconductor device with a cell structure that includes a capacitor with a ferroelectric layer between its electrodes, allowing for polarization reversal with specific saturated polarization voltages, and transistors for data writing and reading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a conventional capacitor is used to retain electric charge in memory cells, then the device structure is simple, but the data retention time is short and reading accuracy decreases due to charge leakage
Solution Approach 1:
The patent changes the material parameter of the capacitor dielectric from conventional materials to ferroelectric materials, which have unique hysteresis characteristics that enable long-term charge retention. The ferroelectric layer maintains polarization state without requiring continuous power supply, thereby extending data retention time and improving reading accuracy.
Solution Approach 2:
The patent employs a composite capacitor structure combining ferroelectric materials with electrode layers and tunnel barriers. This composite structure leverages the high dielectric constant and hysteresis properties of ferroelectric materials to achieve superior charge retention characteristics compared to conventional single-material capacitors.
2Duration of action of stationary object
If high voltage is applied to the ferroelectric layer to achieve polarization reversal, then data retention is improved, but the risk of breakdown increases
Solution Approach 1:
The patent introduces tunnel barrier layers as intermediary structures between the ferroelectric layer and the electrode. These barrier layers mediate the electrical field distribution, allowing high voltage to be applied for polarization reversal while preventing direct contact and potential breakdown between the ferroelectric material and the electrode.
Solution Approach 2:
The patent designs the capacitor structure with protective tunnel barrier layers in advance before applying high voltage for polarization reversal. These pre-installed barrier layers cushion against voltage spikes and prevent breakdown, enabling safe operation at high voltages.
3Duration of action of stationary object
If the capacitor structure is enhanced to improve charge retention, then data retention time increases, but the device complexity increases
Solution Approach 1:
The patent achieves improved data retention by changing the material parameter of the capacitor dielectric to ferroelectric materials, which inherently possess long charge retention capabilities. This material parameter change provides the desired performance improvement without requiring complex structural modifications.
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 semiconductor device achieves long-term data retention, reduced power consumption, and the ability to apply high voltages, while maintaining high reliability and accuracy.
Implementation Method 1
polarization reversal occurs in the ferroelectric layer by application of a first saturated polarization voltage or a second saturated polarization voltage whose polarity is different from a polarity of the first saturated polarization voltage
Data Source
AI summary
Provided is a semiconductor device capable of retaining data for a long time. The semiconductor device includes a cell provided with a capacitor, a first transistor, and a second transistor; the capacitor includes a first electrode, a second electrode, and a ferroelectric layer; the ferroelectric layer is provided between the first electrode and the second electrode and polarization reversal occurs by application of a first saturated polarization voltage or a second saturated polarization voltage whose polarity is different from that of the first saturated polarization voltage; and the first electrode, one of a source and a drain of the first transistor, and a gate of the second transistor are electrically connected to one another. In a first period, the first saturated polarization voltage is applied to the ferroelectric layer. In a second period, a voltage having a value between the first saturated polarization voltage and the second saturated polarization voltage is applied to the ferroelectric layer as a data voltage.