The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Thin Film Technology for Chemical Sensors

Antti J. Niskanen

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Electrical Engineering for public examination and debate in Large Seminar Hall of Micronova at the Aalto University School of Electrical Engineering (Espoo, Finland) on the 27th of January 2012 at 12 noon.

Overview in PDF format (ISBN 978-952-60-4451-4)   [1015 KB]
Dissertation is also available in print (ISBN 978-952-60-4450-7)

Abstract

Microfabrication and thin film technologies were applied in the fabrication of miniaturized chemical sensors. Two types of devices were developed: an electrochemiluminescence device utilizing tunnel-emitted hot electrons, and a microhotplate semiconductor gas sensor with an atomic layer deposited (ALD) tin dioxide sensing film.

The hot electron-induced electrochemiluminescence (HECL) device is an integrated microelectrode device that combines an insulator-covered working electrode and a platinum counter electrode on a single chip. Two types of fluidic systems were integrated on the same type of electrode chip: either an enclosed sample chamber made of polydimethylsiloxane (PDMS) elastomer, or hydrophobic sample confinement on the chip surface. Different metals were tested as the working electrode, and different types of insulator films made by various methods were tested as the tunneling dielectric, to determine the optimal working electrode structures for HECL. These were then used in the integrated microelectrode devices, which were fabricated on silicon and glass substrates. A variety of electrode geometries were tested with the different fluidic systems, and sub-nanomolar sensitivity and wide dynamic range were demonstrated with the best devices. Ongoing work with polymeric substrates is briefly presented.

In the review, latest results are presented on the restoration of the hydrophilic properties of enclosed PDMS microfluidic channels. While a PDMS surface quickly reverts to its naturally hydrophobic state, thus preventing capillary filling, this plasma treatment enables capillary filling even after extended periods of storage.

The gas sensor is a microhotplate (MHP) device, utilizing a tin dioxide sensing layer deposited by ALD for the first time in a MHP sensor. Unconventional solutions were developed for the fabrication sequence to accommodate the demands of the deposition method. Also, metallizations and intermetal dielectrics not commonly used in MHP devices were tested to enable rapid processing of prototype devices with available methods and equipment. Fast response to various analyte gases, as well as good recovery and short-term stability were observed, demonstrating the potential of ALD tin dioxide films in gas sensor applications.

This thesis consists of an overview and of the following 6 publications:

  1. Qinghong Jiang, Johanna Suomi, Markus Håkansson, Antti J. Niskanen, Miia Kotiranta, and Sakari Kulmala. 2005. Cathodic electrogenerated chemiluminescence of Ru(bpy)32+ chelate at oxide-coated heavily doped silicon electrodes. Analytica Chimica Acta, volume 541, numbers 1-2, pages 159-165. © 2004 Elsevier. By permission.
  2. Johanna Suomi, Markus Håkansson, Qinghong Jiang, Miia Kotiranta, Mika Helin, Antti J. Niskanen, and Sakari Kulmala. 2005. Time-resolved detection of electrochemiluminescence of luminol. Analytica Chimica Acta, volume 541, numbers 1-2, pages 167-169. © 2004 Elsevier. By permission.
  3. A. J. Niskanen, T. Ylinen-Hinkka, S. Kulmala, and S. Franssila. 2009. Ultrathin tunnel insulator films on silicon for electrochemiluminescence studies. Thin Solid Films, volume 517, number 19, pages 5779-5782. © 2009 Elsevier. By permission.
  4. Antti J. Niskanen, Tiina Ylinen-Hinkka, Matti Pusa, Sakari Kulmala, and Sami Franssila. 2010. Deposited dielectrics on metal thin films using silicon and glass substrates for hot electron-induced electrochemiluminescence. Thin Solid Films, volume 519, number 1, pages 430-433. © 2010 Elsevier. By permission.
  5. A. J. Niskanen, T. Ylinen-Hinkka, S. Kulmala, and S. Franssila. 2011. Integrated microelectrode hot electron electrochemiluminescent sensor for microfluidic applications. Sensors and Actuators B: Chemical, volume 152, number 1, pages 56-62. © 2010 Elsevier. By permission.
  6. Antti J. Niskanen, Aapo Varpula, Mikko Utriainen, Gomathi Natarajan, David C. Cameron, Sergey Novikov, Veli-Matti Airaksinen, Juha Sinkkonen, and Sami Franssila. 2010. Atomic layer deposition of tin dioxide sensing film in microhotplate gas sensors. Sensors and Actuators B: Chemical, volume 148, number 1, pages 227-232. © 2010 Elsevier. By permission.

Errata of publications 3, 4, 5 and 6

Keywords: ultrathin insulating films, electrochemiluminescence, microhotplate gas sensor, atomic layer deposition

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Last update 2012-10-31