Initial development of a pyroelectric microcalorimeter for applications in x-ray spectroscopy with the quantum ferroelectric potassium tantalum(1-x) niobium(x) oxygen(3)

We are investigating the use of a cryogenic pyroelectric microcalorimeter for X-ray spectroscopy. This type of detector takes advantage of the temperature dependence of the surface charge in ferroelectric and pyroelectric materials to detect the energy of a single absorbed photon or particle. This type of sensor should have advantages over traditional resistive microcalorimeters by having minimal self heating and a reduction of Johnson noise. Several properties of candidate materials are important to its operation as a microcalorimeter. We have measured the dielectric permittivity and parallel resistance of a number of candidate materials as functions of static electric field, temperature and frequency. From these measurements we then picked one of the materials the mixed-crystal quantum ferroelectric KTa{dollar}sb{lcub}rm 1-x{rcub}{dollar}Nb{dollar}sb{lcub}rm x{rcub}{dollar}O{dollar}sb3{dollar} (KTN) for more extensive studies. These included measuring the response of the surface charge to infrared light, alpha particles and changes in temperature. These measurements show the complex nature of KTN with a nonlinear dependence on a static electric field across the device. From these measurements we were able to obtain the pyroelectric response and pyroelectric coefficient as well as the heat capacity of this material. We have shown that the signal response is a function of the sample thickness in KTN and that the surface layers responsible for the geometry dependence reduce the signal from that expected from measured bulk properties. If these surface layers are reduced, then a microcalorimeter comparable to that made with resistive sensors is possible in a thin device.