There is disclosed acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and a piezoelectric plate having parallel front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. A thickness of the interleaved fingers of the IDT is greater than or equal to 0.85 times a thickness of the diaphragm and less than or equal to 2.5 times the thickness of the diaphragm.