CMOS-Compatible Tungsten IR Emitter for NDIR Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing thermal IR sources fabricated using polysilicon or platinum heaters are not compatible with CMOS processes, leading to instability and increased fabrication costs, while separate IR emitters and detectors in NDIR sensors result in low sensitivity due to short optical paths.
Innovation Solution
A CMOS-compatible IR source using a tungsten resistive heater on a dielectric membrane with a Ti/TiN liner, integrated with a CMOS-based IR detector on the same chip, allowing for reliable high-temperature operation and reduced fabrication costs, with an array of micro-hotplates for improved stability and selectivity, and an integrated IR filter for enhanced sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polysilicon or platinum heaters are used in thermal IR sources, then high-temperature operation is achieved, but CMOS process compatibility is lost and fabrication costs increase
Solution Approach 1:
The patent changes the material parameter from polysilicon or platinum to tungsten, which has a higher melting point and better thermal stability at elevated temperatures. This material substitution enables operation at temperatures above 400°C while maintaining CMOS process compatibility, as tungsten can be deposited using standard CMOS-compatible techniques such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).
Solution Approach 2:
The patent employs a composite heater structure consisting of tungsten combined with a Ti/TiN liner layer. The Ti/TiN liner provides adhesion to the underlying substrate and diffusion barrier properties, while the tungsten core provides high-temperature resistance. This composite structure enables the heater to withstand temperatures above 400°C without degrading, while remaining compatible with CMOS fabrication processes.
2Ease of manufacture
If separate IR emitters and detectors are used in NDIR sensors, then device fabrication is simplified, but sensitivity decreases due to short optical paths
Solution Approach 1:
The patent merges the IR emitter and detector into a single integrated device structure. The emitter and detector are positioned in close proximity on the same substrate, with the optical path formed by reflective surfaces within the device housing. This integration maintains fabrication simplicity while extending the effective optical path length through multiple reflections, thereby enhancing gas sensing sensitivity without requiring complex external optical components.
3Temperature
If polysilicon heaters are used above 400°C, then high-temperature operation is achieved, but device stability deteriorates due to resistance drift
Solution Approach 1:
The patent changes the heater material from polysilicon to tungsten, fundamentally altering the thermal and electrical stability parameters. Tungsten exhibits minimal resistance drift at temperatures above 400°C due to its crystalline structure and high melting point, whereas polysilicon suffers from significant resistance changes. This material substitution maintains dimensional and electrical stability during high-temperature operation, ensuring reliable device performance.
Solution Approach 2:
The patent employs a composite heater structure consisting of tungsten combined with a Ti/TiN liner layer. The Ti/TiN liner provides adhesion to the underlying substrate and diffusion barrier properties, while the tungsten core provides high-temperature resistance. This composite structure enables the heater to withstand temperatures above 400°C without degrading, while remaining compatible with CMOS fabrication processes.
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 provides stable, cost-effective IR sources and detectors with improved mechanical stability, sensitivity, and selectivity, enabling efficient gas sensing with reduced noise and extended device lifetime.
Implementation Method 1
A CMOS-compatible IR source using a tungsten resistive heater
Implementation Method 2
thermal Infra-Red (IR) source using a micro-hotplate
Implementation Method 3
A CMOS-compatible IR source using a tungsten resistive heater on a dielectric membrane with a Ti/TiN liner
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An IR source is provided in the form of a micro-hotplate device comprising a CMOS metal layer made of at least one layer of embedded on a dielectric membrane supported by a silicon substrate. The device is formed in a CMOS process followed by a back etching step. The device is advantageous over state of the art devices as it provides a micromachined IR source capable of achieving high temperatures (and thus higher emissions), while at the same time can be fabricated by commercial CMOS processes - thus having low fabrication cost, high reproducibility and reliability and offering the possibility of monolithic integrated circuitry. The device can also be integrated with an IR detector on the same chip and packaged to form a complete NDIR sensor.