Silicon Micromachined Ultrasonic Transducers

This paper presents a novel type of ultrasonic transducer that is made by silicon micromachining. Transducers for both air‐borne and immersion applications are made from parallel plate capacitors whose dimensions are controlled through traditional integrated circuit manufacturing methods. Typical dimensions of the capacitors are: gap =1 micron (vacuum or air), membrane thickness =1 micron (silicon nitride or polysilicon), and diameter =50 microns. A large number of small elements are connected in parallel to make a transducer. Transducers for air‐borne ultrasound applications have been operated in the frequency range of 1–11 MHz, while immersion transducers have been operated in the frequency range of 1–20 MHz. Theoretical modeling calculations of the transducers and their electrical input impedances will be presented. The theory predicts a dynamic range of over 140 dB for both air and immersion applications. Different processing methods for fabricating the transducers and the merits of the different appr...