RESUMO
The detectivity D* limits of YBa(2)Cu(3)O(7-x) bolometers on 0.05-cm-thick crystalline substrates are investigated, and a method to increase D* to greater than 10(9) (cm Hz(1/2))/W at a 20-microm wavelength is proposed. Because the response increases proportionally with the bias current I(b), whereas the noise near T(c) (the transition or critical temperature) of our MgO and SrTiO(3) substrate samples does not, an increase in D* of these samples is obtained by an increase in I(b). Another limiting factor is the dc thermal conductance G(0) of the device, which, although controlled by the substrate-holder thermal boundary resistance for our samples, can be changed by means of thinning the substrate to increase D*. The optimal amount of thinning depends on the substrate's thermal parameters and the radiation modulation frequency. D* in our samples is also found to follow the spectral-radiation absorption of the substrate material.