Infra Red Emitters & detectors using
a common CMOS MEMS technology
platform
Syed Zeeshan Ali
26th October 2016
Confidential © ams AG 2015
Overview
• Gas Sensors technologies are becoming increasingly important in a large number of applications including
home, office, industry and automotive.
• Silicon based sensors offer:
• Small size
• Low Cost
• Low Power consumption
• 3 Silicon based devices for gas sensing based on the same CMOS MEMS technology:
• Resistive gas sensor
• InfraRed Emitter – for NDIR gas sensing
• InfraRed Detector – for NDIR gas sensing
2
Air Quality: A Serious Problem
3
Effects of Poor IAQ
Air Quality
Indication
POOR
VOC Level
High
VOC Effects
Long Term Exposure:
Carcinogenic, Lungs,
Liver, Kidney & Central
Nervous System
damage
CO2 Level above
outdoor level
Health Effects (Nausea,
Headache, Dizziness)
> 2500 ppm
Eye, Nose, Throat, Skin
Irritation, Headaches,
Nausea, Dizziness
MODERATE
Medium
GOOD
Low
CO2 Effects
Significant Impairment of
Performance & DecisionMaking*
Eye, Nose, Throat, Skin
Irritation, Headaches,
Nausea, Dizziness
1000 – 2500 ppm
Moderate DecisionMaking Fatigue,
Impairment and
Concentration*
No impact
< 1000 ppm
No impact on health or
decision making
4
Gas Sensor Applications
Home
Office
Car
5
RESISTIVE GAS SENSORS
NON-DISPERSIVE INFRA RED (NDIR) SENSORS
NDIR COMPONENT: IR EMITTER
NDIR COMPONENT: IR DETECTOR
Confidential © ams AG 2015
Page 6
CMOS Resistive Gas Sensor Structure
Sensing
material
Sensing
Electrodes
Heat
Spreading
Plate
Passivation
5μm
Silicon
Dioxide
Tungsten
Heater
• Fabricated using CMOS
technology
• Post processing steps:
400μm
• Gold Deposition (Electrodes)
• DRIE Back-Etch
7
CMOS Gas Sensor Structure
Membrane
Sensing material
(Metal oxide)
8
Temperature Distribution
K
Only hotplate is heated silicon
remains at ambient (Simulation)
Good thermal uniformity
(M easurement)
9
80
70
60
50
40
30
20
10
0
Transient Time
500
0
100 200 300 400 500 600 700
Temperature (°C)
Temperature (ºC)
Power (mW)
Thermal Properties
400
300
200
100
0
0
25
50
Time (ms)
75
100
10
Stability of micro-heater
Device testing for 3 years and over 900 million on/off cycles
11
Parts Per Billion Response
CCS8xx Response to TVOC at 25OC, 50% RH
5000ppb
1000ppb
300ppb
150ppb
TVOC Gas
a-Pinene
D-Limonene
Acetaldehyde
Acetone
Hexanal
n-Decane
Toluene
Formaldehyde
Benzene
50ppb
Make Up %
1.8%
2.8%
10.4%
33.4%
10.0%
4.6%
3.2%
33.4%
1.6%
12
RESISTIVE GAS SENSORS
NON-DISPERSIVE INFRA RED (NDIR) SENSORS
NDIR COMPONENT: IR EMITTER
NDIR COMPONENT: IR DETECTOR
Confidential © ams AG 2015
Page 13
Non-Dispersive Infra Red Sensor (NDIR)
Basic Principle
Absorption of specific IR wavelength by target gas is
used the determine the concentration of gas.
Predominantly used for CO2 detection
Confidential © ams AG 2015
Page 14
Non-Dispersive Infra Red Sensor (NDIR)
Advantages:
• Is very selective to target gas
• Can be used to measure concentration of unreactive gases
Confidential © ams AG 2015
Page 15
IR Devices based on MEMS Technology
Infrared Emitters:
• Based on Tungsten Micro-Heater made in CMOS
• Advantages to micro-bulbs:
• Small size
• Low Power consumption
• Fast switching times
• Wide Emission Range (2-15μm)
• Applications: NDIR Gas Sensing
Infrared Detectors:
• Based on CMOS Thermopiles
• Use Single Crystal Silicon P+ and N+ materials
• Applications:
• NDIR Gas Sensing
• Gesture Recognition
• People Presence Detection
Confidential © ams AG 2015
Page 16
RESISTIVE GAS SENSORS
NON-DISPERSIVE INFRA RED (NDIR) SENSORS
NDIR COMPONENT: IR EMITTER
NDIR COMPONENT: IR DETECTOR
Confidential © ams AG 2015
Page 17
IR Emitter Cross-Section
Tungsten
Heater
Tungsten
Plate
Passivation
Membrane made of
silicon dioxide and
silicon nitride
Tungsten Heater:
CMOS
Stable at high
temperatures (>500°C)
Silicon
Substrate
Confidential © ams AG 2015
Page 18
IR Emitter Photos
Different Heater Sizes
600μm
800μm
1800μm
Confidential © ams AG 2015
Page 19
IR Emitter Characteristics
450
400
350
300
250
200
150
100
50
0
Emissivity profile
600um
Emissivity
Detected Signal (μV)
Detector voltage vs. Emitter
Temperature
800um
1800um
0
200
400
Temperature (°C)
600
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
2
4
6
8
10
12
Wavelength (µm)
14
Confidential © ams AG 2015
Page 20
16
Plasmonic Layer Structures
Made within the CMOS layers
Tungsten
Heater
Plasmonic
Layer
Silicon
Substrate
Confidential © ams AG 2015
Page 21
Emitter & Detector Spectrum with Plasmonic Layers
Devices optimized for CO2 Detection
Emissivity profile
Emissivity
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
Plasmonic
Non plasmonic
2
4
6
8
10
12
Wavelength (µm)
14
16
IR Emitter: Emissivity at 4.26μm is 0.85,
compared to 0.35 for non-plasmonic device
Confidential © ams AG 2015
Page 22
RESISTIVE GAS SENSORS
NON-DISPERSIVE INFRA RED (NDIR) SENSORS
NDIR COMPONENT: IR EMITTER
NDIR COMPONENT: IR DETECTOR
Confidential © ams AG 2015
Page 23
IR Detector Cross-Section
Made in SOI Process – Based on Thermopiles
Single Crystal Silicon
tracks forming thermocouples
Passivation
Diode
Substrate
Confidential © ams AG 2015
Page 24
IR Detector Top View
Chip Size: 1.76x1.76mm
Membrane Size: 1.3x1.3mm
Confidential © ams AG 2015
Page 25
IR Detector Characterisation
Characterised using a blackbody source
Detector output vs. BB temperature
7
Detector output mV
6
5
4
3
2
1
0
0
20
40
60
80
100
120
Blackbody Temperature (°C)
Confidential © ams AG 2015
Page 26
Summary
Metal Oxide based Gas sensors:
• Fabricated in CMOS technology
• CMOS process with Tungsten Metallization
• Post Process of Gold deposition and back side DRIE.
• Sensitivity down to 50ppb of TVOC
NDIR Sensors:
• Based on Physical effect, or IR absorbtion
• High Selectivity
• Predominantly used for CO2 detection
• Also used for other gases
Infrared Emitters:
• Based on CMOS process with Tungsten Metallization
• Plasmonic layers can be used to improve emission
Infrared Detectors:
• Based on CMOS Thermopiles
• Use Single Crystal Silicon Thermopiles
• Integrated diode for accurate cold junction temperature measurement
Confidential © ams AG 2015
Page 27
Thank you
Please visit our website www.ams.com
Confidential © ams AG 2015