An Integrated Microheater Array With Closed-Loop Temperature Regulation Based on Ferromagnetic Resonance of Magnetic Nanoparticles.

Magnetic nanoparticles (MNP) can generate localized heat in response to an external alternating magnetic field, a unique capability that has enabled a wide range of biomedical applications. Compared with other heating mechanisms such as dielectric heating and ohmic heating, MNP-based magnetic heating offers superior material specificity and minimal damage to the surrounding environment since most biological systems are non-magnetic. This paper presents a first-of-its-kind fully integrated magnetic microheater array based on the ferromagnetic resonance of MNP at Gigahertz (GHz) microwave frequencies. Each microheater pixel consists of a stacked oscillator to actuate MNP with a high magnetic field intensity and an electro-thermal feedback loop for precise temperature regulation. The four-stacked/five-stacked oscillator achieves >19.5/26.5 V measured RF output swing from 1.18 to 2.62 GHz while only occupying a single inductor footprint, which eliminates the need for additional RF power amplifiers for compact pixel size (0.6 mm × 0.7 mm) and high dc-to-RF energy efficiency (45%). The electro-thermal feedback loop senses the local temperature and enables closed-loop temperature regulation by controlling the biasing voltage of the stacked oscillator, achieving a measured maximum/RMS temperature error of 0.53/0.29 °C. In the localized heating demonstration, two PDMS membranes mixed with and without MNP are attached to the microheater array chip, respectively, and their surface temperatures are monitored by an infrared (IR) camera. Only the area above the inductor (∼0.03 mm) is efficiently heated up to 43 °C for the MNP-PDMS membrane, while the baseline temperature stays <37.8 °C for the PDMS membrane without MNP.