A Cryosystem for Optical Evaluation of the Normal Metal Hot-elctron Microbolometer

We are presenting our recent results in development of a direct detector of submillimeter waves (bolometer) based on a microscopic power sensor coupled to an integrated antenna. An electrical NEP of 5×10 W/Hz at 0.1 K has been demonstrated in a dc measurement. A detailed description of design of a cryogenic system for optical evaluation of this detector is presented. Introduction In this report we present our recent results in development of an antenna-coupled direct detector of submillimeter wave radiation – the normal metal hot electron bolometer (NHEB). Broadband submillimeter direct detectors (bolometers) are desired in certain fields of radio astronomy where large bandwidth and high sensitivity requirements are more important than a very sharp spectral resolution. An example of such a field is the study of the relict cosmic microwave background (CMB) radiation. Currently there are several projects where new kinds of structures are proposed as alternative to the present blackbody bolometers with thermistors [1-3]. Increase of the power resolution is one objective in the new development, since the new space-borne telescope projects are going to make available cold low-noise reflectors and thus create room for detectors with better sensitivity level than today’s NEP ≈ 10 W/Hz. The other objective is to decrease the reaction time by at least one order of magnitude from the present level around 10 s. The third objective is to develop a detector technology that will make possible to build large (over 100 pixels) imaging camera arrays of detectors, preferably on a single substrate. Electrical NEP measurements The normal metal hot-electron bolometer has been proposed by M. Nahum et al in [4] and [5]. It is a microscopic power sensor containing a resistive absorber where a highfrequency current induced in a planar integrated antenna is converted to heat, which is then detected as change in the electron gas temperature. The operating principle is shortly explained in the Fig. 1.