Schottky-Ohmic Source MOSFET Structure for High On-State Current
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Solution Overview
Problem
Schottky source-drain MOSFETs suffer from small on-state current and large off-state leakage current, limiting their commercial applications due to the Schottky barrier suppressing electron carrier transport and preventing the formation of a complete electron conduction channel.
Innovation Solution
The structure of Schottky source-drain MOSFETs is improved by combining an Ohmic source electrode with a Schottky source electrode, with the Ohmic electrode interposed between the gate insulating film and the Schottky electrode, forming an MIS junction to facilitate a complete electron conduction channel under a positive gate bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky barrier is formed between the source electrode and semiconductor to achieve normally-off functionality, then the device can be turned off by reverse-biasing the Schottky barrier, but the on-state current is suppressed due to the Schottky barrier height limiting electron carrier transport
Solution Approach 1:
The source electrode is divided into two distinct portions: a first portion that forms a Schottky barrier contact with the semiconductor layer to enable normally-off functionality, and a second portion that forms an Ohmic contact to provide high carrier concentration and facilitate strong on-state current. This segmentation allows each portion to fulfill its specific function without compromise.
Solution Approach 2:
Different regions of the source electrode are assigned different contact properties: the first portion (Schottky contact) provides the barrier necessary for normally-off operation, while the second portion (Ohmic contact) provides high conductivity for strong on-state current. This local differentiation of contact quality resolves the contradiction between needing a barrier for turn-off and needing high conductivity for turn-on.
2Length of moving object
If a Schottky barrier is used to suppress source-drain punch-through and short-channel effects, then device miniaturization is enabled, but the on-state current remains limited due to the Schottky barrier
Solution Approach 1:
The source electrode is segmented into Schottky and Ohmic portions, allowing the Schottky barrier to suppress punch-through and short-channel effects in miniaturized devices while the Ohmic portion ensures sufficient on-state current is achieved despite the reduced device dimensions.
Solution Approach 2:
The Ohmic contact portion acts as an intermediary that bridges the Schottky barrier region to the channel, providing a high carrier concentration reservoir that feeds electrons into the channel without being blocked by the Schottky barrier, thus maintaining strong on-state current in scaled devices.
3Ease of manufacture
If a pure Schottky source electrode is used to simplify the manufacturing process, then ion implantation and high-temperature annealing are eliminated, but the on-state current is severely limited
Solution Approach 1:
The source electrode is segmented into two portions that can be formed in a single metal deposition step without requiring ion implantation or high-temperature annealing. The Schottky portion provides normally-off functionality while the Ohmic portion ensures high on-state current, achieving both manufacturing simplicity and electrical performance.
Solution Approach 2:
The contact properties are changed by varying the metal material or work function across different portions of the source electrode. This parameter change allows one portion to form a Schottky barrier while another forms an Ohmic contact, achieving dual functionality without complex processing steps.
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 modified MOSFET achieves a large on-state current capability comparable to pn-junction MOSFETs, maintaining normally-off functionality and simplifying the manufacturing process, suitable for ampere-level currents and mass production.
Implementation Method 1
A Schottky barrier is formed between a first portion of the source electrode and the n-type semiconductor layer
Implementation Method 2
a second portion of the source electrode contacts the n-type semiconductor layer to form an Ohmic contact
Implementation Method 3
A gate insulating film interposed between the gate electrode and the n-type semiconductor layer
Data Source
Figure 1~3a
Figure 3b~4
Figure 5a~5b
AI summary
This disclosure relates to the technical field of semiconductors. Through localized design optimization of the structure of existing Schottky-junction MOSFETs, the disclosure proposes a novel field-effect transistor possessing both large on-state current capability and normally-off functionality. The field-effect transistor disclosed herein comprises: an n-type semiconductor layer; a drain electrode; a source electrode; a gate electrode; and a gate insulating film. A Schottky barrier exists between a first portion of the source electrode and the n-type semiconductor layer, while a second portion of the source electrode contacts the n-type semiconductor layer forming an Ohmic contact. The on-state current capability of the field-effect transistor of the disclosure matches or even exceeds that of a pn-junction MOSFET under equivalent conditions.