The effect of silicon substrate thickness on the performance of thin film PZT pyroelectric detectors is theoretically and experimentally investigated. As the silicon substrate thickness increases, the pyroelectric current responsivity drastically decreases. The current responsivity of a pyroelectric thin film detector with no silicon substrate is about two orders higher than that of a similar detector with 450 mum thick silicon substrate. To verify the theoretical analysis, micromachined Pb(Zr0.3Ti0.7)O-3 (PZT30/70) thin film pyroelectric detectors with different silicon substrate thickness are fabricated and characterised. The experimental results agree well with the theoretical analysis. (C) 2002 Elsevier Science Ltd. All rights reserved.