Development and Comprehensive Evaluation of TMR Sensor-Based Magnetrodes

TL;DR

This paper presents the development and evaluation of TMR sensor-based magnetrodes designed for local magnetic field detection in the brain, achieving high sensitivity and low detection limits suitable for neuronal signal measurement.

Contribution

The study introduces TMR magnetrodes with optimized design features, demonstrating superior sensitivity and detection capabilities compared to existing GMR-based sensors.

Findings

Achieved a limit of detection of 300pT/Hz1/2 at 1 kHz.

Demonstrated capability to detect neuronal magnetic signals with minimal averaging.

Optimized magnetrode design enhances local magnetic field detection.

Abstract

Due to their compact size and exceptional sensitivity at room temperature, magnetoresistance (MR) sensors have garnered considerable interest in numerous fields, particularly in the detection of weak magnetic signals in biological systems. The magnetrodes, integrating MR sensors with needle-shaped Si-based substrates, are designed to be inserted into the brain for local magnetic field detection. Although recent research has predominantly focused on giant magnetoresistance (GMR) sensors, tunnel magnetoresistance (TMR) sensors exhibit significantly higher sensitivity. In this study, we introduce TMR-based magnetrodes featuring TMR sensors at both the tip and mid-section of the probe, enabling detection of local magnetic fields at varied spatial positions. To enhance detectivity, we have designed and fabricated magnetrodes with varied aspect ratios of the free layer, incorporating diverse junction shapes, quantities, and serial arrangements. Utilizing a custom-built magnetotransport and noise measurement system for characterization, our TMR-based magnetrode demonstrates a limit of detection (LOD) of 300pT/Hz1/2 at 1 kHz. This implies that neuronal spikes can be distinguished with minimal averaging, thereby facilitating the elucidation of their magnetic properties.