Table 1
Thickness and composition of deposited layers
		Nominal	Impedance	Longitudinal
Function	Material	thickness (nm)	(MRayl)	velocity (ms−1)
Top electrode	AlCu	130	17	6,420
	W	120	101	5,230
Piezo layer	AlN	1300	37	10,400
Bottom electrode	W	170	101	5,230
	AlCu	200	17	6,420
Coupling layer	SiO2	500	13	5,970
Seal to PSi	Amorphous Si	20	20	8,400
Porous layer/multilayers	PSi	variable	variable	variable

Aliev et al. Nanoscale Research Letters 2012 7:378   doi:10.1186/1556-276X-7-378