Low Temperature Effects: Surface Mount Capacitors

Abstract

The low signal to noise ratio produced by the VLPC (Visible Light Photon Counter) chip in the detection of a single photon necessitates the use of a filtering capacitor. Maximum performance of the filtering capabilities dictate the placement of the capacitor be as close to the VLPC chip as possible. However, the chip operates at extremely low temperatures (7K). In addition, available space within the VLPC cassette is limited. Therefore it is desired to find a capacitor which provides good temperature stability at cryogenic temperatures within a minimal space (e.g. surface mounted). This engineering note presents the results from a test of the effect of low temperature on surface mounted capacitors. Preliminary testing suggested that capacitors of the tantalum type would provide the best te mperature stability at cryogenic temperatures, therefore two different tantalum capacitors were tested. A ceramic capacitor was also included in the results as a comparison, even though preliminary results suggested the ceramic type would not provide sufficient temperature stability.