Highly Near-Infrared-Sensitive, Printed Flexible Thermistors. Austin Shearin ext Brewer Science Inc.

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1 Highly Near-Infrared-Sensitive, Printed Flexible Thermistors Austin Shearin ext Brewer Science Inc.

2 Brewer Science Mission Deliver innovation and value through our unique culture by helping the people and customers we serve to succeed Dr. Terry Brewer, President/CEO and Founder Brewer Science Headquarters Rolla, Missouri, USA Established in 1981

3 What We Do

4 Brewer Science Sensors Current available sensors: InFlect TM Thermistor InFlect TM Moisture InFlect TM Flex

5 Infrared (IR) Sensor Introduction Modification of the thermistor with an infrared absorbing layer and aluminum reflecting back layer

6 Comparison with Commercial IR Sensors Commercial IR sensors Uses thermocouple as reference Accuracy dependent on thermocouple Wavelength generally > 5 µm Filters and lenses used to eliminate UV and visible spectrum and focus light to small sensor region Operating temp -20 C to 100 C generally Currently: $2 - $50 per sensor Fully screen-printed IR sensors Standalone sensor Accuracy dependent on sensor Shows response from near infrared to far infrared Currently, no filters or lenses used Operating temp dependent on substrate and encapsulation. Up to 400 C possible. Currently: < $1 per sensor. Cost can drop more when switching to roll-to-roll manufacturing

7 Fully Screen Printed IR Sensor Design Screen printing allows for different designs, sizes, and form factors Substrate can be easily changed Process is transferrable to roll-to-roll manufacturing process Can be integrated into larger printed electronics projects with multiple sensor per sheet Encapsulation Substrate Aluminum S IR-absorbing layer CNT layer D

8 Carbon Nanotube Thermistor Carbon nanotubes (CNTs) have very high carrier concentration and mobility due to the sp 2 hybridized orbitals Majority of resistance in CNT film comes from junction resistance between tubes which can be modelled as highly conductive materials separated by quantum barriers Increased thermal energy lowers the quantum barriers, effectively decreasing the resistance of the film

9 Temperature Response Tested in environmental chamber with constant humidity of 35% RH Linear response with over 99% goodness of fit Temperature coefficient of resistance: ppm/ C Hysteresis: < 2.0 C Accuracy: < 2.2 C

10 Temperature Response Time The thermistor was dipped into a 100 C oil bath to measure the response time A resistance change of 22% was measured and a response time of < 250 ms was recorded

11 Temperature Selectivity Over Humidity Drift for 20% to 80% RH change: 0.11% Drift for 20C/80% RH/10 hr.: 1.7%

12 IR Sensing Test Equipment Blackbody source used to generate infrared radiation Optical chopper used to open/close blackbody source Resistance recorded using multimeter Distance d=32 mm d= 0

13 IR Sensor Response The sensor has a 30 second off/on/off cycle to measure the response The blackbody source was 800 C, which has a peak wavelength of 2.70 µm The total change in resistance is close to 11% The response time is close to 5 seconds

14 IR Sensor Sensitivity vs Blackbody Temperature The sensor was positioned 39 mm from the blackbody source Temperature of the blackbody source and peak wavelength of radiation are listed on the graph Peak infrared radiation is in the short-wavelength and midwavelength infrared region

15 IR Sensor Sensitivity vs Blackbody Temperature The sensor was moved to 32 mm from the blackbody source to get a higher irradiance on the sensor Peak wavelength reaches longwavelength infrared before dropping below a 1% change in resistance

16 IR Sensor Sensitivity vs Distance from Source The blackbody temperature was held at 300 C for a peak wavelength of 5.06 µm and increased the distance of the sensor from the blackbody source The sensor reaches a maximum distance of 98 mm with a 0.4% change in resistance with an irradiance of 1.22 W/m 2

17 IR Sensor Directionality The aluminized backside reflects the IR radiation and allows for directionality of the sensor The blackbody source was held at 800 C and two sensors were measured for the front and back side at a distance of 39 mm from the source Approx. an 11:1 and 9:1 ratio of front- to back-side signal is achieved for the two sensors respectively

18 Summary InFlect TM thermistors have a temperature coefficient of resistance of ppm/ C and a response time of < 250 ms, and were modified with an IR absorbing layer to create an IR sensor Sensors are hermetically sealed with an encapsulation layer so the sensor is temperature selective IR sensors show response from the short-wavelength to long-wavelength infrared regions with a response time close to 5 seconds Detection was possible up to 10 cm away from the source without the use of lenses Directionality is achieved using an aluminum back coating

19 THANK YOU QUESTIONS?