In the automotive and industrial automation sectors there is a growing demand for new intelligent control systems that reduce energy consumption and emissions and improve the life cycle management of the components. At the same time, the emergent complexity of control systems has introduced a need for a new type of embedded sensing integrated into the components of the system to control operations in a favourable way. This has made smart sensing materials essential in the development of detection and control of the operational conditions in vehicles and equipment.
The advantage of piezoresistive hard carbon thin film material is its high sensitivity to temperature and strain when compared to conventional metallic temperature and strain gauge sensors. As less than a micrometre thick amorphous carbon semiconductor film, it can be embedded to surfaces of mechanical components for the function of sensing and supervising conditions in several applications. The low temperature deposition process developed for the hard carbon sensors enables the use of wide variety of dielectric materials, even heat sensitive plastics, as substrates.
“Piezoresistive hard carbon sensors can bring smart supervisory control to future machines, examples such as sense of touch to a robotic hand or pressure and temperature sensing to limit overload,” Kolehmainen states.
Hard carbon sensors, when applied on steel substrates, have to be isolated from the electrically conductive substrate. In his dissertation Kolehmainen studied feasibility of aluminium oxide based coatings deposited by APS and HVOF thermal spray and by PVD RF-sputtering for the electrical insulation.
In his study he demonstrated successfully that it is possible to deposit functional piezoresistive hard carbon thin film sensors on steel substrates using thermal spray aluminium oxide coatings for the electrical insulation as-deposited without post-treatment needed. Measurements of thermistor beta value and gauge factor of the hard carbon thin film sensor elements are encouraging for future development work of embedded sensors with performance on aluminium oxide coatings comparable to that measured earlier on smooth polyimide substrates.
Jukka Kolehmainen is currently working as R&D manager at Oerlikon Balzers Coating Finland Oy in Espoo where he continues research and development of functional thin film coatings.
Public defence on Friday 6 October
The doctoral dissertation of MSc (Tech) Jukka Kolehmainen in the field of surface engineering in material science titled Aluminium Oxide Coatings for Electrical Insulation of Hard Carbon Thin Film Sensors will be publicly examined at the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Friday 6th of October 2023 at Hervanta campus, Konetalo, auditorium K1702 (Korkeakoulunkatu 6, Tampere). The Opponents will be Privatdozent, Dr. Lutz-Michael Berger from Fraunhofer Institute IKTS and Vice President, Professor Erja Turunen from VTT Technical Research Centre of Finland. The Custos will be Professor Emeritus Petri Vuoristo from the Faculty of Engineering and Natural Sciences at Tampere University
The doctoral dissertation is available online.
The public defence can be followed via remote connection.
Photo: Harri Vornanen