Due to low power operation, intrinsic integrability and compatibility with CMOS processing, aluminum nitride (AlN) piezoelectric (PZE) microcantilevers are a very attractive paradigm for resonant gas sensing. In this paper, we theoretically investigate their ultimate limit of detection and enunciate design rules for performance optimization. The reduction of the AlN layer thickness is found to be critical. We further report the successful development and implementation in cantilever structures with a 50 nm thick active PZE AlN layer. Material characterizations demonstrate that the PZE e(31) coefficient can remain as high as 0.8Cm(-2). Electrically transduced frequency responses of the fabricated devices are in good agreement with analytical predictions. Finally, we demonstrate the excellent frequency stability with a 10(-8) minimum Allan deviation. This exceptionally low noise operation allows us to expect a limit of detection as low as 53 zg mu m(-2) and demonstrate the strong potential of AlN PZE microcantilevers for high resolution gas detection.