In collaboration with the University of Twente (Low Temperature Division), Micronit developed a glass micro cryogenic cooler. Within the project, Micronit was responsible for the process development of the chip. The micro cooler consists of a stack of three fusion bonded borosilicate glass wafers and has a total thickness of approximately 700 µm. The manufacture process has 7 mask steps and over 100 process steps.

Application
The chip can be used for electronic circuitry cooling, which can improve the signal-to-noise ratio and bandwidth of a system. The combination of the knowledge and the different technologies used within Micronit enabled the team to develop a chip with high accuracy. Thanks to the use of batch processing the cost per unit were relatively low. The excellent collaboration between Micronit and the University of Twente succeeded in a functional cooling device, optimized for effectiveness.

P.P.P.M. Lerou, G.C.F. Venhorst, C.F. Berends, T.T. Veenstra, M. Blom, J.F. Burger, H.J.M. ter Brake and H. Rogalla
Low Temperature Division, University of Twente, Enschede, The Netherlands and Micronit Microfluidics BV, Enschede, The Netherlands (2006).
Journal of Micromechanics and Microengineering, 2006, 16, 1919-1925.

Abstract
This paper describes the design and production process of a variety of reliable micro cryogenic coolers. The different cold stages are based on an optimized design found during a study which was done to maximize the cold-stage effectiveness. Typical cold-stage dimensions are 30 × 2 × 0.5 mm with an expected net cooling power varying from 10 mW to 20 mW at a tip temperature of 96 K. A cold stage consists of a stack of three fusion bonded D263T glass wafers. The production process has 7 lithography steps and roughly 100 process steps. In order to determine the maximum bend, shear and bond stresses inside a 175 µm thick D263T glass wafer, several pressure tests were performed.