About the rupture of nitride membrane, here's some information for you about
our experience at Caltech.

For 3x3 mm2, low-stress nitride, 1-2,000 A diapgragm, the rupture pressure is
as high as 30 psi. These diaphragms have been used for X-ray microscopy.

For 8x8 mm2, 1-um low-stress nitride diaphragm, it's about 20 psi.

For 1x1 mm2, 1.5-um diaphragm, the highest pressure we observed is 70 psi.

However, the burst pressure depends on the quality of the nitride and the
boundary conditions a lot. In general, the fracture strength of the thin-film
low-sstress nitride is around 3-4%.