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Design, Fabrication and Optimization of Thermal Radiation Detectors Based on Thin Polymer Membranes
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Sensorgruppen, STC)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The number of applications in which infrared radiation sensors are used is increasing. In some applications, the cost of the sensor itself is an issue, and simple solutions are thus required. In this thesis, the investigations have related to the use of thin polymer membranes in thermal infrared sensors, such as bolometers and thermopiles.

Infrared sensors are usually subcategorized into photonic sensors and thermal sensors. For detection of infrared radiation using a photodetector, there is a requirement for low band-gap material. The need of cooling makes infrared photodetectors rather expensive, and not an alternative for low-cost applications. In thermal sensors, the heat generated from the incident infrared radiation is converted into an electrical output by means of a heat sensitive element. Thermal sensors operate at room temperature, which makes them a low-cost alternative. The basic structure of thermal sensors consists of a temperature sensitive element connected to a heat sink through a structure with low thermal conductance. It is common to use thin membranes of Silicon or Silicon Nitride as thermal insulation between the heat sink and the sensitive element. In comparison, polymers have a thermal conductance that is lower than in these materials, and this increases the generated temperature in the sensitive element. A polymer such as SU-8 has a low thermal conductivity and is applied using a spin coater. This reduces the number of complex processing steps. This thesis presents a new application of SU-8 as a closed membrane in a thermal sensor.

The concept was initially demonstrated by fabricating a nickel bolometer and titanium/nickel thermopile structure with a 5 µm SU-8 / SiO2 membrane. However, for the sensor responsivity to be able to compete with commercial thermal sensors the structures, some optimization was required. Since the thermopile generates its own voltage output and requires no external bias, the optimizations were focused on this structure. There exist a number available software tools for thermal simulation of components. However, to the author’s best knowledge, there exist no tool for design optimization of thermopiles with closed membranes. An optimization tool using iterative thermal simulations was developed and evaluated. A new thermopile structure, based on the optimization results, was both fabricated and characterized. Using an infrared laser with a small spot, the measured responsivity of the manufactured thermopile was higher than that of a commercial sensor. In the case of a defocused spot and for longer wavelengths, the infrared absorption in the absorption layer reduces and degrades the responsivity.

The thermopile was further evaluated as a sensor in a carbon dioxide meter application based on the NDIR principle. An increase in the CO2 concentration demonstrated a clear decrease in the thermopile voltage response, as was expected. By normalizing the voltage response and comparing it with a commercial sensor, this showed that the SU-8 based thermopile is relatively more sensitive to changes in the CO2 concentration.

Place, publisher, year, edition, pages
Sundsvall: Kopieringen Mittuniversitetet , 2009. , 64 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 73
Keyword [en]
Thermal detector, Polymer, Membrane, SU-8
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-9579ISBN: 978-91-86073-46-6 (print)OAI: oai:DiVA.org:miun-9579DiVA: diva2:233047
Public defence
2009-09-19, O111, Holmgatan 10, Sundsvall, 13:15 (English)
Opponent
Supervisors
Projects
STC
Available from: 2009-08-28 Created: 2009-08-27 Last updated: 2011-02-06Bibliographically approved
List of papers
1. Thermal simulation and design optimization of a thermopile infrared detector with SU-8 membrane
Open this publication in new window or tab >>Thermal simulation and design optimization of a thermopile infrared detector with SU-8 membrane
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2009 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 19, no 5, 055016- p.Article in journal (Refereed) Published
Abstract [en]

Simulation and optimization tools are commonly used in the design phase of advanced electronics devices. In this work, we present a thermal simulation and design optimization tool for infrared thermopile detectors based on a closed membrane structure. The tool can be used to simulate and optimize thermopile detectors with an arbitrary number of design parameters. The optimization utilizes the Nelder–Mead and the adaptive simulated annealing optimization algorithms to maximize the system performance. A thermopile detector with an SU-8-based closed membrane and metal–metal thermocouples has been simulated and optimized. Based on the results generated by the tool, an optimized detector has been fabricated and characterized. The results from the measurements presented are in good agreement with the simulation results.

Keyword
Simulation, Optimization, thermopile, membrane
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-8828 (URN)10.1088/0960-1317/19/5/055016 (DOI)000265580900026 ()2-s2.0-68249138779 (Scopus ID)
Projects
STC - Sensible Things that Communicate
Available from: 2009-04-29 Created: 2009-04-29 Last updated: 2016-10-05Bibliographically approved
2. Fabrication and characterization of a design optimized SU-8 thermopile with enhanced sensitivity
Open this publication in new window or tab >>Fabrication and characterization of a design optimized SU-8 thermopile with enhanced sensitivity
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2009 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 20, no 11, 115202- p.Article in journal (Refereed) Published
Abstract [en]

In the infrared wavelength region, thermopiles are an important type of detectors. A major advantage of thermopiles is their non-cooling requirement. Depending on the applied absorption layer, their responsivity is often rather flat within a large wavelength region. This work presents the fabrication and characterization of a sensitivity and design optimized thermopile detector with a 4 µm self-supported SiO2/SU-8 membrane. The structure consists of 240 series interconnected thermocouple junctions obtained by a metal evaporation and lift-off. Two metal combinations have been evaluated, namely, nickel/titanium and aluminium/bismuth. Series resistances of 76 k and 283 k were measured for the Ni/Ti thermopile and the Al/Bi thermopile respectively. For the Al/Bi thermopile a responsivity of 60 V/W was achieved using a 1.56 µm fibre coupled diode laser with a power of 3.5 mW. Using a white light source with a radiation flux of 0.45 W/mm2 a voltage response of 68 V mm2/W was measured for the Al/Bi thermopile. The time constant of the characterized detectors was calculated as being 70 ms, using the pulsed IR laser.

Place, publisher, year, edition, pages
IOP, 2009
Keyword
Fabrication, Thermopile, SU-8
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-8829 (URN)10.1088/0957-0233/20/11/115202 (DOI)000270988800022 ()2-s2.0-70350691206 (Scopus ID)
Conference
6th International Symposium on Measurement Techniques for Multiphase Flows, Dec 15-17, 2008, Okinawa, Japan
Projects
STC - Sensible things that communicate
Note
6th International Symposium on Measurement Techniques for Multiphase Flows, DEC 15-17, 2008, Okinawa, JapanAvailable from: 2009-04-29 Created: 2009-04-29 Last updated: 2016-10-05Bibliographically approved
3. Design of a Micromachined Thermopile Infrared Sensor with a Self-Supported SiO2/SU-8 Membrane
Open this publication in new window or tab >>Design of a Micromachined Thermopile Infrared Sensor with a Self-Supported SiO2/SU-8 Membrane
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2008 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 8, no 12, 2044-2052 p.Article in journal (Refereed) Published
Abstract [en]

In the infrared region of the spectrum thermoelectric detectors such as the thermopile, are extensively used. These detectors rely on the well-known Seebeck effect, in which there is a direct conversion of thermoelectric differentials into electrical voltage. The temperature difference over thermocouple junctions is in general, created by forming a thin membrane connected to the silicon bulk. In many existing thermopiles, materials such as Si and Si3N4 have been used as membrane. These materials suffer from relatively high thermal conductivity, which lowers the membrane temperature and reduces the sensitivity of the detector. A material such as SU-8 2002 has a much lower thermal conductivity and is applied using standard photolithographic processing steps. This work presents thermal simulations regarding the use of SU-8 2002 as a thermal insulating membrane as compared to Si and Si3N4. The simulation results presented show that the temperature increase in a 5 µm SiO2/SU-8 membrane is about 9% higher than in a 1 µm Si3N4 membrane, despite the membrane thickness being increased by a factor of 5. A thermopile consisting of 196 serially interconnected Ti/Ni thermocouples positioned on a 5 µm SiO2/SU-8 2002 membrane has been fabricated. The sensitivity of the fabricated device has been evaluated in the infrared region, using a 1.56 µm IR laser and a xenon arc lamp together with a monochromator. The measurement results show a sensitivity of approximately 5 V/W over the wavelength range between 900 - 2200 nm. Measurements performed in a vacuum chamber show that the sensitivity of the detector could be increased by more than a factor of 3 by mounting the detector in a vacuum sealed capsule.

Place, publisher, year, edition, pages
Piscataway, USA: IEEE, 2008
Keyword
Infrared sensor, self-supported membrane, SU-8, thermopile
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-6971 (URN)10.1109/JSEN.2008.2007679 (DOI)000261545600037 ()2-s2.0-85008020303 (Scopus ID)
Projects
STC - Sensible Things That Communicate
Note

VR-Ecology

Available from: 2008-11-16 Created: 2008-11-11 Last updated: 2017-07-04Bibliographically approved
4. Fabrication and evaluation of a thermal sensor formed on a thin photosensitive epoxy membrane with low thermal conductivity
Open this publication in new window or tab >>Fabrication and evaluation of a thermal sensor formed on a thin photosensitive epoxy membrane with low thermal conductivity
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2008 (English)In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, Institute of Physics (IOP), 2008, 082048- p.Conference paper, Published paper (Refereed)
Abstract [en]

This article present the fabrication and development of a thin metal film bolometer IR detector connected in a Wheatstone bridge configuration. The bolometer is constructed on a 4 μm thin self-supported SU-8 2002 membrane. A polymer material such as SU-8 has low thermal conductivity and is applied using standard photolithographic processing step, and this could increase detector sensitivity and lower the production cost. Thermal simulation results are presented, which verifies SU-8 as a better choice of materials compared to common membrane materials such as Si and Silicon nitride. Measurements on the fabricated nickel resistance bolometer on SU-8 2002 membrane show a sensitivity of 9.3 V/W when radiated by an IR laser with a wavelength of 1.56 μm.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2008
Series
Journal of Physics: Conference Series (Online Edition), ISSN 1742-6596 ; 100
Keyword
Bolometer, SU-8, IR, infrared, thermoelectric
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-359 (URN)10.1088/1742-6596/100/8/082048 (DOI)000275655200326 ()5036 (Local ID)5036 (Archive number)5036 (OAI)
Conference
17th International Vacuum Congress/13th International Conference on Surface Science/Internatinal Conference on Nanoscience and Technology, Jul 02-06, 2007, Stockholm, Sweden
Projects
STC - Sensible Things that Communicate
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2016-10-05Bibliographically approved
5. Development of an infrared thermopile detector with a thin self-supporting SU-8 membrane
Open this publication in new window or tab >>Development of an infrared thermopile detector with a thin self-supporting SU-8 membrane
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2007 (English)In: 2007 IEEE SENSORS, VOLS 1-3, New York: IEEE conference proceedings, 2007, 836-839 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we present the development and characterization of thermopile detector on a 4 mum thin self-supporting membrane made of the epoxy based photoresist SU-8. The membrane is realized using silicon bulk micromachining techniques. In many existing thermopile detectors, a temperature difference over the thermocouple junctions is achieved by connecting a thin membrane of either Si or Si3N4 to a silicon bulk. These materials suffer from relatively high thermal conductivity, which lowers the sensitivity of the detector. A material such as SU-8 has much lower thermal conductivity and is applied using standard photolithographic processing steps. Simulation results are presented which verifies SU-8 as a better choice than Si and Si3N4 when used as thermal insulating membrane in a thermopile detector. A thermopile consisting of 196 series coupled Ti/Ni thermocouples has been fabricated. Results from measurements are presented, showing a sensitivity of 5.6 V/W and a noise equivalent power (NEP) of 9.9 nW/radicHz.

Place, publisher, year, edition, pages
New York: IEEE conference proceedings, 2007
Series
IEEE Sensors, ISSN 1930-0395 ; 9
Keyword
Thermopile, SU-8, IR
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-358 (URN)10.1109/ICSENS.2007.4388531 (DOI)000254563600213 ()5035 (Local ID)978-1-4244-1262-4 (ISBN)5035 (Archive number)5035 (OAI)
Conference
6th IEEE Sensors Conference, Oct 28-31, 2007, Atlanta
Projects
STC - Sensible Things that Communicate
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2016-10-05Bibliographically approved
6. Experimental evaluation of a thermopile detector with SU-8 membrane, in a carbon dioxide meter setup
Open this publication in new window or tab >>Experimental evaluation of a thermopile detector with SU-8 membrane, in a carbon dioxide meter setup
Show others...
2009 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 9, no 12, 1633-1638 p.Article in journal (Refereed) Published
Abstract [en]

Continuous control of the carbon dioxide levels in the ventilation systems in office buildings and public schools has been shown to increase productivity and save money. However, these measurement systems require further developments in order to be more cost effective. This paper presents an evaluation of an Al/Bi thermopile detector with a 4 µm thin SiO2/SU-8 membrane in a CO2 meter application using the NDIR (Non-Dispersive Infrared Technology). The system consists of an 11 cm aluminum tube, used as the sample chamber and in which a light source and a thermopile detector with a 4.26 µm optical bandpass filter are positioned on its opposite sides. The light source is pulsed with a frequency of 0.5 Hz. The voltage response of the Al/Bi thermopile is measured for different CO2 concentrations, and, as expected according to the Lambert-Beer law, there is an exponential decrease in the measured intensity. The absolute response is about 50 % lower than for a commercial HMS J21 thermopile from Heimann Sensor GmbH. In relative terms, on the other hand, the Al/Bi thermopile is more sensitive for changes in the CO2 concentration. At 7500 ppm, the voltage response has decreased to 40 % of the reference response measured in the nitrogen atmosphere.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-8830 (URN)10.1109/JSEN.2009.2030645 (DOI)000271020700003 ()2-s2.0-70350637523 (Scopus ID)
Projects
STC - Sensible things that communicate
Available from: 2009-04-29 Created: 2009-04-29 Last updated: 2016-10-05Bibliographically approved

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