Non-Volatile Memory Charge Storage Layer for Low-Voltage Retention
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Solution Overview
Problem
Existing non-volatile memory cells using high dielectric constant films face challenges in improving retention characteristics and operating voltage, leading to trade-offs in reliability and efficiency.
Innovation Solution
A semiconductor device with a non-volatile memory cell featuring a charge storage layer composed of two insulating films, HSO1 and HSO2, where the hafnium concentration and bandgap of HSO1 are lower than those of HSO2, allowing for improved charge retention and reduced operating voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high dielectric constant film is used as the charge storage layer, then the operating voltage can be reduced, but the retention characteristics deteriorate
Solution Approach 1:
The charge storage layer is divided into two distinct insulating films (first insulating film with higher Hf concentration and smaller bandgap, second insulating film with lower Hf concentration and larger bandgap). This segmentation allows each film to perform specialized functions: the first film reduces operating voltage through high dielectric constant, while the second film improves retention characteristics through larger bandgap and lower trap density.
Solution Approach 2:
Different regions of the charge storage layer are assigned different material compositions and properties. The first insulating film (closer to gate electrode) has higher Hf concentration for voltage reduction, while the second insulating film (closer to semiconductor substrate) has lower Hf concentration for better charge retention. This local differentiation resolves the contradiction between voltage reduction and retention improvement.
2Use of energy by moving object
If the hafnium concentration in the charge storage layer is increased to reduce operating voltage, then the dielectric constant increases, but the bandgap decreases leading to worse retention characteristics
Solution Approach 1:
The charge storage layer is segmented into two films with different Hf concentrations. The first film has higher Hf concentration to provide high dielectric constant for voltage reduction, while the second film has lower Hf concentration to provide larger bandgap for retention improvement. This resolves the contradiction by spatially separating the conflicting requirements.
Solution Approach 2:
Different Hf concentrations are applied locally within the charge storage layer. The region closer to the gate electrode uses high Hf concentration for voltage reduction, while the region closer to the substrate uses low Hf concentration for retention. This local quality differentiation allows simultaneous optimization of both parameters.
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 proposed solution enhances the retention characteristics of the memory cell while reducing the operating voltage, thereby improving the overall reliability and efficiency of the semiconductor device.
Implementation Method 1
a non-volatile memory cell using a high dielectric constant film such as a hafnium oxide film instead of the silicon nitride film as the charge storage layer
Implementation Method 2
a bandgap of the third insulating film is larger than a bandgap of the fourth insulating film
Data Source
AI summary
A memory cell which is a non-volatile memory cell includes a gate insulating film having a charge storage layer capable of retaining charge and a memory gate electrode formed on the gate insulating film. The charge storage layer includes a first insulating film containing hafnium and silicon and a second insulating film formed on the first insulating film and containing hafnium and silicon. Here, a hafnium concentration of the first insulating film is lower than a hafnium concentration of the second insulating film, and a bandgap of the first insulating film is larger than a bandgap of the second insulating film.