Field-Effect Transistor Gate Electrode Structure to Curb Skin Effect
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Solution Overview
Problem
The use of conductive materials containing high melting point metals like tungsten or molydenum in gate electrodes leads to increased gate resistance due to the skin effect, impairing high-frequency characteristics in field effect transistors.
Innovation Solution
A method of manufacturing a field effect transistor that involves forming a recessed region in the cap layer and using a gate electrode structure with a main portion made of a high conductivity material and a gate electrode barrier layer made of a conductive material that prevents diffusion into the barrier layer, thereby curbing the skin effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive material containing high melting point metal (tungsten or molybdenum) is used for the gate electrode to prevent diffusion, then reliability is improved, but gate resistance increases due to skin effect, worsening high-frequency characteristics
Solution Approach 1:
The gate electrode is segmented into two distinct layers: a lower layer made of high melting point metal (tungsten or molybdenum) for diffusion prevention, and an upper layer made of highly conductive metal (gold or platinum) for low resistance. This segmentation allows each layer to fulfill its specific function independently, resolving the contradiction between reliability and high-frequency characteristics.
Solution Approach 2:
The gate electrode uses a composite structure combining two different materials with complementary properties: the high melting point metal provides diffusion barrier functionality, while the highly conductive metal provides low resistance for high-frequency operation. This composite approach allows the system to achieve both reliability and good high-frequency characteristics simultaneously.
2Productivity
If a fine gate length is employed to improve high-frequency characteristics, then productivity is improved, but manufacturing precision becomes more difficult to achieve
Solution Approach 1:
The invention changes the material parameters of the gate electrode by using highly conductive metal (gold or platinum) with resistivity of 2.4×10^-8 to 1.0×10^-7 Ω·m. This parameter change allows achieving low gate resistance even at fine gate lengths, enabling high-frequency operation without requiring extremely precise manufacturing control.
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 effectively reduces the skin effect in the gate electrode, thereby enhancing the high-frequency characteristics and reliability of the field effect transistor.
Implementation Method 1
a gate electrode barrier layer formed of a conductive material that prevents the gate electrode material from diffusing into the barrier layer
Implementation Method 2
a conductivity thereof is not very high (resistivity is high). In particular, in a high-frequency operation, a so-called skin effect in which an applied signal propagates only on a surface of the gate electrode becomes a problem
Data Source
AI summary
A gate electrode includes a main portion formed of a gate electrode material, and a gate electrode barrier layer disposed between the main portion and a barrier layer and formed of a conductive material that prevents the gate electrode material from diffusing into the barrier layer. A surface of the main portion in a region above a first insulating layer faces a periphery without a layer of the conductive material being formed.