Drain-extended transistor drift surface layer hot electron injection
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Solution Overview
Problem
High voltage transistors, particularly drain-extended transistors, face reliability issues due to hot electron injection, which can alter their characteristics and lead to device failure under high voltage conditions.
Innovation Solution
Incorporating a highly doped drift surface layer from the gate to the drain contact in the transistor design helps stabilize the transistor's characteristics, such as linear region current, even when compromised by hot electron injection, by distributing the electric field and reducing the impact of hot electrons on the oxide insulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a long drift region is used to distribute voltage and avoid breakdown, then breakdown voltage is improved, but hot electron injection into the oxide insulator increases causing transistor characteristic degradation
Solution Approach 1:
The patent applies local quality by creating a drift surface layer with different doping characteristics than the bulk drift region. This layer has higher doping concentration near the surface, which modifies the electric field distribution specifically in the region where hot electrons are generated and injected, without changing the overall long drift region structure needed for high breakdown voltage.
Solution Approach 2:
The patent changes the doping concentration parameter by forming a drift surface layer with higher doping concentration (1E16 to 1E18 atoms/cm³) compared to the bulk drift region. This parameter change modifies the electric field profile and reduces hot electron injection while maintaining the high breakdown voltage through the extended drift region structure.
2Power
If high voltage is applied to achieve desired power performance, then power capability is improved, but hot electron generation and injection increase causing device failure
Solution Approach 1:
The patent converts the harmful effect of high electric fields into a beneficial outcome by using the drift surface layer to control where and how electric field energy is dissipated. The higher doping concentration in the surface layer creates a controlled path for carrier generation and recombination that reduces hot electron injection into the oxide, while still allowing high voltage operation for power capability.
3Stability of the object's composition
If the drift region is extended to improve voltage distribution, then electric field distribution is improved, but the area susceptible to hot electron injection increases
Solution Approach 1:
The patent addresses this by adding a vertical dimension to the solution through the drift surface layer. Rather than changing the lateral area of the drift region, the invention modifies the vertical doping profile by creating a surface layer with different characteristics, thus controlling hot electron injection without reducing the necessary drift region area for voltage distribution.
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 solution enhances the stability and reliability of the transistor under reverse bias conditions, maintaining acceptable operation even when affected by hot electron injection, with improved breakdown voltage and current stability.
Implementation Method 1
This long drift region distributes an applied voltage between the source and drain to avoid localized high electric fields, which can cause breakdown or other damage to the device
Implementation Method 2
Under high voltages, hot electrons can be injected into the oxide insulator on the surface of the drift region. These hot electrons induce holes nearby in the drift region. If enough hot electrons embed in the oxide insulator, the characteristics of the transistor can change
Data Source
AI summary
Described examples include an integrated circuit having a semiconductor substrate. The integrated circuit has a transistor that includes a buried layer having within the substrate, the buried layer defining a drift region between the buried layer and the top surface and a body region in the substrate extending from the buried layer to the surface of the substrate. The transistor also having a source formed in the body region, a drain extending from the buried layer to the surface of the substrate, a drift well extending from the buried layer toward the top surface and extending from the body region to the drain, a drift surface layer located between the drift well and the top, and a gate proximate to the surface of the substrate at the body region.