AlN epitaxial film with atomically flat surface for GHz-band saw devices

We have successfully developed (00·1) AlN film with atomically flat surface on (00·1) sapphire substrate using metalorganic chemical vapor deposition (MO-CVD) method. The atomically flat surface of less than Ra=2Å, Ra means mean roughness measured by atomic force microscope(AFM), within the thickness of 1.7μm has been achieved, whose conditions are high substrate temperature of 1200°C, low pressure of 30Torr, low V-III ratio of 500 and the numerous flow rate of trimethylaluminum (TMA)-back-up H₂ gas of 5.0slm. The temperature-coefficient-of-delay (TCD) of the fabricated surface-acoustic-wave (SAW) device on (00·1) AlN/(00·1)Al₂O₃ combination with atomically flat surface are found to be 44.5ppm/°C at kH=2.25 and 28.5ppm/°C at kH=3.32, where kH is the normalized thickness by wave number, k is wave number and H is AlN film thickness. These measured TCD are agreed with simulated curve. AlN/Al₂O₃ combination with atomically flat surface has a potential for zero-TCD at kH=4.5.