Microbolometer Pixel Ion Implantation VOx Resistivity Control
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Solution Overview
Problem
The existing microbolometer fabrication processes are costly, complex, and yield-limited due to the need for additional metallization steps and poor control over electrical interconnects, especially as pixel sizes shrink, leading to issues with resistance variability and thermal detection efficiency.
Innovation Solution
Ion implantation is used to convert vanadium oxide (VOx) in selected areas to low resistivity mixed phases (V2O3, VO, V) for electrical interconnects, eliminating the need for metal legs and associated processing steps, providing precise control over resistivity and reducing the thermal mass of the microbolometer pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal or metal alloy (NiCr) is used as electrical interconnect, then electrical conductivity is improved, but device complexity and manufacturing cost increase due to additional processing steps
Solution Approach 1:
The patent combines the VOx sensing material with the electrical interconnect function by converting the VOx leg directly into a conductive state through ion implantation, eliminating the need for separate metal interconnect layers and associated processing steps
Solution Approach 2:
The patent changes the electrical parameters of VOx by applying ion implantation (e.g., Ar+, Kr+, Xe+ ions at specific energies and doses) to convert insulating VOx into a conductive mixed-phase vanadium oxide with metal-like conductivity, enabling it to serve as both sensing material and interconnect
2Reliability
If back-sputtering is used to reduce VOx resistance, then electrical conductivity is improved, but manufacturing precision deteriorates due to poor control over conversion depth and excessive erosion
Solution Approach 1:
The patent replaces the mechanical sputtering process with ion implantation, which provides precise control over ion penetration depth through adjustable ion energy parameters, eliminating the uncontrolled erosion and poor depth control inherent in back-sputtering
Solution Approach 2:
The ion implantation process inherently controls the conversion depth through the selected ion energy, where lower energies (e.g., 2.5-40 KeV) provide precise shallow conversion for leg resistance control without eroding the protective dielectric, making the process self-regulating
3Reliability
If additional metallization steps are added, then electrical interconnect quality is improved, but productivity decreases due to increased processing time and yield loss
Solution Approach 1:
The patent merges the VOx deposition and interconnect formation into a single process sequence, where the VOx leg is formed first and then converted to conductive state through ion implantation, eliminating the need for separate metal deposition, photolithography, and etching steps
Solution Approach 2:
The patent discards the traditional metal interconnect materials (NiCr, Al, Cu) and recovers/repurposes the VOx material itself by converting it to a conductive state, thereby eliminating multiple processing steps and associated yield losses
4Length of moving object
If pixel size is reduced, then device miniaturization is achieved, but manufacturing precision deteriorates due to difficulty in maintaining continuous step coverage
Solution Approach 1:
The patent merges the VOx sensing layer and interconnect structure into a unified planar configuration, where the VOx leg extends continuously from the bridge to the contact area without requiring separate metal traces, simplifying the topology and improving step coverage for smaller pixels
Solution Approach 2:
The patent applies local quality by using ion implantation to create different phases of vanadium oxide in different regions: insulating VOx in the sensing bridge area and conductive mixed-phase VOx in the leg and contact areas, enabling functional differentiation without additional materials or complex structures
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 reduces processing steps, improves yield and cost, enhances sensitivity and thermal detection by minimizing thermal conductance, and allows for better scaling to smaller geometries with improved pixel performance and robustness.
Implementation Method 1
Ion implantation is a highly controllable, precise and reproducible process. Ion implantation is a well understood semiconductor processing technique in which accelerated ions are directed onto a material. Two precisely controlled parameters called ion energy (KeV) and ion dose (ions/cm2) determine how deep and how much the material is altered.
Implementation Method 2
Transition metal oxides can be reduced and their resistivity significantly lowered by bombarding them with ions. This same phenomenon can be applied to selective areas of the VOx material originally deposited and convert these areas to low resistivity mixed phase vanadium oxide outside of the sensing area of the bridge.
Implementation Method 3
One type of an infrared detector consists of a microbolometer responsive to the heat energy of infrared radiation.
Implementation Method 4
In certain microbolometers, the pixel bridge is formed from an oxide of vanadium (VOx), which has a high temperature coefficient of resistance (TCR) making it an excellent IR sensing material.
Data Source
AI summary
A microbolometer pixel and a reduced-step process for manufacturing it comprising the step of ion implantation of vanadium oxide whereby VOx is converted to a low resistivity mixed phase vanadium oxide (VOx/V2O3/VO/V) in the leg, metallized support post, and detector contact areas. Masking maintains high temperature coefficient of resistance (TCR) VOx in the sensing portion of the pixel bridge region. The implanted area resistivity and TCR can be controlled by ion implantation dose and energy.