A 14.8-<i>μ</i>W Power and &lt;10-<i>μ</i> T_rms Noise 3-D AC Magnetic Sensor in CMOS for Biomedical Applications

Magnetic sensors are used extensively in applications related to automotives, navigation, medical electronics, and consumer products. Hall sensors are commonly used due to their compatibility with the standard CMOS process but suffer from poor 3-D sensitivity and consume high power. Here, we present the first-of-its-kind 3-D ac magnetic sensor in the CMOS process with high-resolution and ultralow-power operation. The sensor is comprised of three orthogonal and highly dense metal coils (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i>, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i>, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i>) implemented in the 65-nm node, which generate a voltage in response to ac magnetic fields by electromagnetic induction. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> sensor coils are realized in the vertical plane of the CMOS chip by using interconnect vias as part of the coil structure, while the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> sensor is realized in the horizontal plane. The induced voltage by the three coils is processed by a low-noise instrumentation amplifier (IA), sharp bandpass filter (BPF), programmable gain amplifier (PGA), differential peak detect and hold circuit, 12-bit successive approximation register (SAR) analog-to-digital converter (ADC), and serializer. The entire circuitry consumes only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14.8~{\mu }$ </tex-math></inline-formula>W to yield <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>T-level resolution. The sensor is successfully demonstrated for 3-D localization and tracking of catheters with 500-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m mean accuracy in a surgical operation room (OR), which shows significant potential toward clinical translation.