Preamplified planar microcoil on GaAs substrates for microspectroscopy

Abstract

In the course of the publication the design, fabrication, and experimental evaluation of a planar microcoil for nuclear magnetic resonance ͑NMR͒ spectroscopy with a 360 m inner diameter integrated to a low-noise metal-semiconductor field-effect transistor is presented. The impedance matching of the coil and transistor was achieved by adjusted coil geometry, while an appropriate microfabrication process including air bridge contacts and a multilayer metal stack was developed for the necessary susceptibility matching of the coil metallization. The NMR spectra of experiments in an 11.75 T magnet ͑corresponding to 500 MHz͒ show the amplification of the signal by the integrated transistor. Due to previous experiments, we wanted to ensure that the whole signal emerged from the sensitive volume of the microcoil.

NMR probes for measuring magnetic fields and field dynamics in MR systems

“…Depending on the specific wire used the susceptibility match that can be achieved with available fluorocarbons may also not be sufficient. Further susceptibility-matching approaches are based on altering the susceptibility of copper wire by combining and/or plating it with other metals, such as rhodium, aluminum, gold, and titanium (25)(26)(27). However, these approaches imply demanding manufacturing and restrictive assumptions about coil geometry.…”

Microcoil-based MRI: feasibility study and cell culture applications using a conventional animal system

“…In these earlier studies, solenoidal coils were used exclusively. With the advent of modern micro-fabrication technologies such as photolithography and consecutive etching, fabrication of individual microscopic surface coils became possible [12][13][14]. Nowadays, with RF coils sizes on a µm scale, as well as dedicated hardware and optimized methods, highresolution imaging with isotropic voxel sizes down to 3 µm [15] or in-plane resolving of structures of 1 µm width [7] have been reported.…”

Microcoils on Structured Silicon Substrates for Magnetic Resonance Detection

“…Planar spiral microcoils fabricated by lithography and electroplating [3], and solenoidal microcoils constructed by methods including nonplanar lithography, multilayer lithography and self-assembly [4]- [6], have been reported. MR detector coils have been combined with etched troughs to increase coupling to the sample [7], -factors have been increased on glass substrates [8], capacitors [9] and transistors [10] have been integrated on-chip and implantable coils have been developed [11]. Helmholtz coils, which offer increased field uniformity, have also been constructed from stacked substrates [12], [13].…”