The liquid droplet spray device (5) comprises a micromachined substrate (8, 18, 18a 8a, 18, 18a), a space (9) within the substrate for containing a liquid substance (4), means for supplying (7) the liquid (4) to the space (9), and outlet means (13, 14, 15) for ejecting the liquid as a mono-dispersive droplet spray when the liquid undergoes a vibration, The outlet means comprises a pyramid-shaped tapered cavity (13) which is micromachined in the space (9). The outlet means further comprises at least one output nozzle (14) and output channel (15) connecting the tapered cavity (13) to the outlet nozzle (14), the outlet nozzle (14) and the output channel (15) having a non-tapered vertical shape. Thanks to such a device, the exact amount ejected may be determined accurately which allows for a predicted lung deposition of the droplets by using appropriate control means adapted to the kind of patient.
