Infoscience

Thesis

Broadband single-chip transceivers for compact NMR probes

Nuclear magnetic resonance (NMR) is one of the most relevant spectroscopic tools in use today. However, NMR requires relatively expensive and complicated experimental settings given by the combination of high homogeneous magnetic fields and a relatively complex radio-frequency (RF) electronics. This thesis concerns the development of RF electronics hardware, specifically introducing new complementary-metal-oxide-semiconductor (CMOS) transceiver designs. This work stems from a collaboration between EPFL and Metrolab SA, and aims at pushing in two directions: first, NMR-oriented CMOS transceivers will simplify the implementation of NMR probes for both experimental and commercial applications; second, novel CMOS ultra-compact probes will deliver experimental versatility and improved sensing power at the nL and sub-nL scale. We describe broadband 1 mm^2 transceivers operating in the range from 1 MHz to 1 GHz. The microchips include a RF power amplifier, a low-noise RF preamplifier, a frequency mixer, an audio-frequency (AF) amplifier, fully integrated transmit-receive switches, IQ signal generation, and broadband quadrature detection. In this work we show multi-nuclear NMR spectroscopy in combination with excitation/detection probe-heads based on micro-solenoids, therefore validating the broadband functioning. A combination of the transceivers and Metrolab's technology is also shown to deliver state-of-art performance in prototypes of commercial probes aimed for magnetometry. We shown that custom multichannel probes employing water samples of 500 nL are capable of measurement resolutions as high as 0.06 ppb/Hz^(1/2) at 7 T, and that magnetic noise due to field fluctuations can be directly measured at this resolution level and distinguished by the electronic noise. Overall, the results of this package indicate that NMR-oriented CMOS transceivers simplify the implementation of NMR probes for both experimental and commercial applications. When CMOS transceivers are combined to external resonators the resulting NMR probe may be called "compact" in the sense that the overall probe size is dominated by the excitation/detection resonator itself. Besides the implementation of compact probes, in this thesis we introduce the concept of ultra-compact NMR probes, where a single-chip transceiver is co-integrated with a multilayer microcoil realized with the metals of the CMOS technology. We demonstrate that with a non-resonant integrated coil of about 150 µm external diameter a 1H spin sensitivity of about 1.5·10^13 spins/Hz^(1/2) is achieved at 7 T. This value of sensitivity compares well with the most sensitive inductive probes previously reported at similar volume scales, with the resulting device showing an exceptional degree of versatility. We use, for the first time, a ultra-compact CMOS probe for the NMR spectroscopy of intact, static, sub-nL single ova of 0.1 and 0.5 nL, thereby reaching the relevant volume scale where life development begins for a broad variety of organisms, humans included. Thanks to the robustness and the versatility of the probe we could deliver a first extensive study of sub-nL single ova and indicate that ultra-compact probes are promising candidates to enable NMR-based study and selection of microscopic entities at biologically relevant volume scales. Overall, the results of this study indicate that CMOS ultra-compact probes will deliver experimental versatility and improved sensing power at the nL and sub-nL scale.

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