Stabilizing Oxide Semiconductor Threshold Voltage with Negative Fixed Charge
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Solution Overview
Problem
Oxide semiconductor transistors tend to have normally-on characteristics due to oxygen deficiency, leading to unstable threshold voltage control, and silicon carbide or gallium nitride transistors also face challenges in controlling threshold voltage, resulting in unreliable semiconductor devices.
Innovation Solution
A silicon oxide film with a negative fixed charge, containing aluminum or other Group 13 elements, is used in contact with the active layer to create a negative electric field, shifting the threshold voltage in the positive direction and stabilizing the transistor's electric characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an oxide semiconductor film is used as an active layer, then the transistor can be formed over a larger substrate, but oxygen deficiency causes the threshold voltage to shift in the negative direction, resulting in normally-on characteristics
Solution Approach 1:
A silicon oxide film with negative fixed charge is introduced as an intermediary layer between the gate electrode and the oxide semiconductor active layer. This intermediary film generates a negative electric field that compensates for the positive charge caused by oxygen deficiency in the active layer, thereby stabilizing the threshold voltage without affecting the large substrate area capability
Solution Approach 2:
The electrical parameters of the gate insulating film are changed by incorporating a silicon oxide film with controlled negative fixed charge density. This parameter change creates a compensating electric field that offsets the threshold voltage shift caused by oxygen deficiency, enabling stable operation over large substrate areas
2Manufacturing precision
If heat treatment is performed after forming the oxide semiconductor film, then the film structure is improved, but oxygen is released from the film, causing threshold voltage shift and normally-on characteristics
Solution Approach 1:
The silicon oxide film with negative fixed charge is formed before the heat treatment process. This preliminary action ensures that when heat treatment releases oxygen from the oxide semiconductor film, the negative fixed charge in the silicon oxide film is already in place to compensate for any threshold voltage shifts, maintaining stability throughout the manufacturing process
3Speed
If silicon carbide or gallium nitride is used as an active layer, then high field effect mobility is achieved, but the threshold voltage is difficult to control, resulting in normally-on characteristics
Solution Approach 1:
The silicon oxide film with negative fixed charge acts as a mediator between the gate electrode and the high-mobility semiconductor layer (silicon carbide or gallium nitride). This intermediary creates a controllable negative electric field that enables threshold voltage control in these otherwise difficult-to-control materials, while preserving their high field effect mobility characteristics
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 approach enables the manufacture of highly reliable semiconductor devices with stable electric characteristics by effectively controlling the threshold voltage and reducing oxygen deficiency-related issues.
Implementation Method 1
a silicon oxide film having a negative fixed charge refers to a silicon oxide film in which aluminum concentration is greater than or equal to 0.01 at. % and less than or equal to 10 at. %
Implementation Method 2
By using the silicon oxide film having a negative fixed charge as a film in contact with an active layer of a transistor or a film in the vicinity of the active layer, a negative electric field is always applied to the active layer due to the negative fixed charge
Implementation Method 3
a silicon oxide film having a negative fixed charge refers to a silicon oxide film in which aluminum concentration is greater than or equal to 0.01 at. % and less than or equal to 10 at. %
Data Source
AI summary
Provided is a highly reliable semiconductor device by giving stable electric characteristics to a transistor in which a semiconductor film whose threshold voltage is difficult to control is used as an active layer. By using a silicon oxide film having a negative fixed charge as a film in contact with the active layer of the transistor or a film in the vicinity of the active layer, a negative electric field is always applied to the active layer due to the negative fixed charge and the threshold voltage of the transistor can be shifted in the positive direction. Thus, the highly reliable semiconductor device can be manufactured by giving stable electric characteristics to the transistor.