Microelectronic Magnetic Flux Sensor for Hearing Aid Application

A 3-D microelectronic inductor has been fabricated and characterized for use as a magnetic flux sensor, also known as a telecoil, for a hearing aid application. This telecoil was fabricated in a 0.5¿m CMOS process with three metal layers. The 3-D structure is more space efficient than conventional spiral inductors and allows for an optimal number of turns for the space available. The telecoil has an inductance of 80¿H, a resistance of 34k¿, and a capacitance of 275pF. When combined with an CMOS audio amplifier, the telecoil acts as a magnetic flux sensor by picking up the magnetic signal generated by telephone speaker which is then fed into the audio amplifier. The integrated telecoil is smaller in size and can be produced at a lower cost than commercially available telecoils. The electrical response of the telecoil to a changing magnetic field was found to be linear with respect to the input amplitude, and neglecting the noise associated at lower frequencies, independent of frequency. This response is in agreement with theory.