© 2018 Elsevier Ltd An amorphous silicon carbonitride (a-SiCN) diaphragm for environmental cells was developed by magnetic-field- and pulsed-plasma-enhanced chemical vapor deposition using a unique power source of variable pulse parameters. A positive square wave pulse voltage of 500 V in a pulse width range from 10 μs to 500 μs was alternately supplied to the upper and lower of two parallel electrodes for plasma generation with the precursor gases hexamethyldisilazane, Ar, and N2. By supplying pulse voltages alternately to both electrodes, rather than only the upper electrode, the influence of charging could be suppressed. To investigate the effect of the pulse parameter on film nitridation, a-SiCN diaphragms were prepared by three methods of plasma generation: (1) different pulse frequencies with the same pulse width to both electrodes, (2) the same pulse frequency with a different pulse width to both electrodes, and (3) the same pulse width including a no-voltage-supply time to both electrodes. The diaphragm, which was fabricated by supplying a 50-μs pulse width at 10 kHz to both electrodes, had the highest nitrogen component ratio of 28.9%. Enhancement of film nitridation was thought to be due to the increase in the number of collisions of ions in the plasma.