MOSFET Bolometer Structure for Impedance-Matched IR Absorption
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Solution Overview
Problem
Existing bolometer structures with MOS-FET transistors for detecting electromagnetic radiation in the infrared range face suboptimal absorption due to high impedance from doped zones, leading to reduced equivalent resistance and signal-to-noise ratio.
Innovation Solution
The structure incorporates a MOS-FET transistor with specific zone configurations, where the first, second, and third zones are formed as layers with controlled dimensions, reducing their volume and influence on impedance, and using a 'mid-gap' metal for the gate electrode to minimize heat generation and optimize absorption, with the gate electrode covering the third zone's sidewalls to enhance channel width and drain-source current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the first and second zones are highly doped to enable good electrical contact, then electrical contact is improved, but the equivalent resistance perceived by electromagnetic radiation decreases to 1-100Ω/□, which is far from the optimal 376.9Ω/□
Solution Approach 1:
The patent applies local quality by making the doping concentration non-uniform across different zones. The first and second zones have high doping concentrations for good electrical contact, while the third zone has a lower doping concentration (at least 10 times lower) to minimize its impact on equivalent resistance. This spatial variation in doping quality allows simultaneous optimization of both electrical contact and electromagnetic radiation absorption.
Solution Approach 2:
The transistor structure is segmented into three distinct zones with different doping concentrations. This segmentation allows each zone to be optimized for its specific function: the first and second zones for electrical contact, and the third zone for minimizing impedance impact on radiation absorption, thereby resolving the contradiction between good electrical contact and optimal equivalent resistance.
2Manufacturing precision
If the absorbing element is optimized to have impedance close to vacuum (376.9Ω/□), then absorption is improved, but the total impedance of the structure remains lower due to the influence of transistor elements
Solution Approach 1:
The patent optimizes the local quality of the third zone by using low doping concentration, which minimizes its contribution to the total impedance. This allows the absorbing element to maintain its optimized impedance of 376.9Ω/□ while the third zone's low doping ensures it does not significantly reduce the overall equivalent resistance, thereby improving total structure absorption.
Solution Approach 2:
The third zone acts as an intermediary between the highly doped first and second zones and the absorbing element. Its low doping concentration mediates the electrical connection while minimizing its impact on the equivalent resistance, allowing the absorbing element's optimized impedance to be preserved in the total structure.
3Productivity
If the gate electrode covers the third zone to enhance channel width, then drain-source current is improved, but heat generation may increase affecting absorption
Solution Approach 1:
The gate electrode is positioned to cover the third zone laterally, enhancing the channel width and drain-source current. The low doping concentration in the third zone reduces Joule heating in this region, mitigating the heat generation issue while still benefiting from the enhanced channel width provided by the gate coverage.
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 configuration optimizes electromagnetic radiation absorption and drain-source current, achieving an equivalent impedance closer to that of vacuum, thereby improving the signal-to-noise ratio and sensitivity of the detection structure.
Implementation Method 1
an absorbing element configured to absorb the electromagnetic radiation
Implementation Method 2
detecting temperature rise of said absorbing element upon absorbing the electromagnetic radiation
Implementation Method 3
a transducer having a characteristic which varies with temperature, the transducer being associated with the absorbing element for detecting temperature rise
Implementation Method 4
a gate electrode, the gate electrode covering the third zone along at least one side wall of the third zone
Data Source
AI summary
The invention concerns an electromagnetic radiation detection structure (10) comprising at least one absorbing element defining an absorption plane, and a MOSFET transistor (100). The transistor comprises: at least one first and at least one second zone (111, 112) of a first type of conductivity; at least one third zone (113) separating the first and second zones (111, 112) from each other; and a gate electrode. The first zone (111), the third zone (113) and the second zone (112) are formed respectively by a first, a third and a second layer that extend in the absorption plane parallel to each other and are arranged one after another in a direction perpendicular to the absorption plane. The gate electrode covers the third zone (113) along at least one lateral wall of said third zone (113).