Low-cost route for the definition of IDE (interdigitated electrode) structures with nanometric geometries over large areas
Microsystems
Final Report Abstract
Sensors with inter-digitated electrodes are devices for various purposes. They have a simple structure, but a high sensitivity asks for metallic electrodes well below a micrometre and a quite large area of the inter-digitated electrode field. Then the preparation of an inter-digitated sensor requires costly lithography and etching processes typical of state of the art Si technology; this renders the production of such devices beyond the scope of small and medium enterprises. Therefore, an alternative low-cost route for the production of inter-digitated sensors with large areas and nanometre-scaled electrodes was investigated, a route without the need for costly vacuum equipment, sophisticated lithography techniques and high-end materials. The concept uses standard contact lithography, standard photoresists, thermal nanoimprint and sputtering and is not restricted to Si substrates. The preparation procedure is as follows: the substrate of choice is provided with a thin photoresist layer; the resist is locally pre-exposed to tune the viscosity of the material for the subsequent imprint step that defines the nanometre-scaled electrode field. A second lithography step defines the contacts of the device. Simple development removes the resist in the contact and electrode areas so that the complete metal structure can be obtained by sputtering, without a dry etching step in between. Lift-off of the resist defines the final device. To make this concept work the interplay between exposure and temperature treatment with a photoresist had to be studied in detail to define a suitable process window, where the local modification of the viscosity of a negative tone photoresist by partial exposure defines the imprint depth obtained in a thermal nanoimprint process and thus the respective residual layer thickness; after full exposure, a residual layer thin enough is still developable, a thicker one remains and protects the substrate during sputtering. This effect is used to connect alternating electrodes to the contact. All basic steps necessary for sensor preparation were demonstrated successfully; their combination to prepare a real device with inter-digitated electrodes was hampered by the funding available, which prohibited the purchase of the specific stamps and photomasks with the sensor geometries required. Nonetheless the project was able to demonstrate a low-cost route for the preparation of sensors with inter-digitated electrodes based on nanoimprint, optical lithography and sputtering, without sophisticated high-end technology. When polymeric replica stamps are used for thermal imprint, all process steps can be performed similarly well on low-cost polymeric substrates.
Publications
- “Resist reflow minimization via viscosity control by exposure”, Journal of Vacuum Science and Technology 31(6) 06FB051 (2013)
Khalid Dhima, Christian Steinberg, Andre Mayer, Si Wang, Marc Papenheim, and Hella-Christin Scheer
- “Competitiveness of negative tone resists for nanoimprint lithography”, Microelectronic Engineering 123, 43–47 (2014)
Khalid Dhima, Christian Steinberg, Andre Mayer, Si Wang, Marc Papenheim and Hella-Christin Scheer
(See online at https://doi.org/10.1016/j.mee.2014.05.017) - “Residual layer lithography”, Microelectronic Engineering 123, 84-88 (2014)
Khalid Dhima, Marc Papenheim, Christian Steinberg, Si Wang, Hella- Christin Scheer
(See online at https://doi.org/10.1016/j.mee.2014.05.008) - “Hybrid lithography –The combination of T-NIL & UVL”, PhD Thesis, Der Andere Verlag GmbH, ISBN: 9783862475025 (2015)
Khalid Dhima
- “Nanoimprint combination techniques”, Microelectronic Engineering 141, 92-101 (2015)
Khalid Dhima, Christian Steinberg, Si Wang, Marc Papenheim and Hella- Christin Scheer
(See online at https://doi.org/10.1016/j.mee.2015.01.039)
