Comparison of Si3N4-SiO2 and SiO2 Insulation Layer for Zero-Bias CMUT Operation Using Dielectric Charging Effects
Abstract:
In this letter, we report the characteristics of zero-bias capacitive micromachined ultrasonic transducers (CMUTs) in various aspects, considering the transmission and reception sensitivity and evaluation of the long-term stability with ac transmission in immersion. The main idea of the zero-bias CMUT implementation is that the charge is injected by the dielectric charging effects in an insulation layer in the pull-in state. The CMUT was fabricated by a local oxidation of silicon (LOCOS) process, and the insulation layer consists of Si3 N4 -SiO2 and SiO2, which have been commonly used in previous studies. A study on the charging effects is reported to quantitatively observe the voltage shift by charge transfer with time dependence at different temperatures and collapsing time dependence. Therefore, we successfully implemented a zero-bias CMUT with a transmission efficiency of 4.62 kPa/V at a center frequency of 7.53 MHz in Si3 N4-SiO2 and a transmission efficiency of 6.78 kPa/V at a center frequency of 7.86 MHz in SiO2 immersion.
Related Concept Videos
Dielectric Polarization in a Capacitor
Electrostatic Boundary Conditions in Dielectrics
Consider a case where both the mediums across a boundary are two different dielectric materials. Recall that the electric field and electric displacement are proportional and related through the material's permittivity....
Metal-Semiconductor Junctions
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
MOS Capacitor
The metal gate is typically made from highly conductive materials such as aluminum or polysilicon. Beneath the metal gate lies a thin layer of...
Capacitor With A Dielectric
Dielectrics are non-conducting materials with no free or loosely bound electrons. When a dielectric is...
Biasing of Metal-Semiconductor Junctions
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...


