A single chip electron spin resonance detector based on a single high electron mobility transistor

Single-chip microwave oscillators are promising devices for inductive electron spin resonance spectroscopy (ESR) experiments on nanoliter and subnanoliter samples. Two major problems of the previously reported designs were the large minimum microwave magnetic field (0.1 mT to 0.7 mT) and large power consumption (0.5 mW to 200 mW), severely limiting their use for the investigation of samples having long relaxation times and for operation at low temperatures. Here we report on the design and characterization of a single-chip ESR detector operating with a microwave magnetic field and a power consumption orders of magnitude lower compared with previous designs. These significant improvements are mainly due to the use of a high electron mobility transistor (HEMT) technology instead of a complementary metal-oxide-semiconductor (CMOS) technology. The realized single-chip ESR detector, which operates at 11.2 GHz, consists of an LC Colpitts oscillator realized with a single high-electron mobility transistor and a co-integrated single turn planar coil having a diameter of 440 μm. The realized detector operates from 300 K down to 1.4 K, at least. Its minimum microwave magnetic field is 0.4 μT at 300 K and 0.06 μT at 1.4 K, whereas its power consumption is 90 μW at 300 K and 4 μW at 1.4 K, respectively. The experimental spin sensitivity on a sensitive volume of about 30 nL, as measured with a single crystal of α,γ-bisdiphenylene-β-phenylallyl (BDPA)/benzene complex, is of 8×10^(10) spins/Hz^(1/2) at 300 K and 2×10^(9) spins/Hz^(1/2) at 10 K, respectively. In a volume of about 100 pL, located in proximity to the coil wire, the spin sensitivity improves by two orders of magnitude.

Electron Spin Resonance detectors from 400 MHz to 360 GHz

Alessandro Valentino Matheoud

Methods based on the electron spin resonance (ESR) phenomenon are non-invasive tools adopted to investigate paramagnetic systems at temperatures ranging from above 1000 K to below 1 K. Since 2008, the group of Dr. Boero has been working on a detection technique based on the integration of ESR sensors on single chips. The proposed methodology allowed to study samples in the nanoliter scale and reach a spin sensitivity at least two orders of magnitude better than the best commercially available spectrometers. The detection principle can be summarized as follows. An ESR sensitive sample is placed in close proximity to the planar inductor of an LC oscillator operating at microwave frequency. In presence of a suitable static magnetic field, the ESR phenomenon takes place. It causes a variation in the sample magnetization which translates to a variation of the inductance, leading to both a frequency shift of the oscillator (frequency detection) and a variation of the oscillation amplitude (amplitude detection). Consequently, the ESR phenomenon may be detected by tracking the operating point of the oscillator. In this thesis, I investigate the application of the aforementioned detection principle in the range from 400 MHz to 360 GHz. Firstly, a semi-integrated solution operating from 400 MHz to 610 MHz is developed for an industrial application (CTI project). In such context, the originality of the work stands in the implementation of a completely standalone portable scanner for contactless inspection which may also be used for ferromagnetic (FMR) applications and zero-field measurements. Secondly, a set of single-chip ESR detectors working from 10 GHz to 146 GHz and based on CMOS technologies are characterized from 300 K down to 10 K. Here, an ESR experiment at a frequency as high as 360 GHz can be performed thanks to the fourth harmonic signal generated by a 90 GHz detector. Conversely, the 10 GHz detector shows the best noise performance and allows to achieve the record distance resolution of 0.3 pm when used as a proximity sensor. After that, the possibility of using integrated technologies based on HEMTs is investigated so as to overcome the main limitations of the CMOS based detectors: (1) the high power consumption which denies their use below 10 K and (2) the saturation issue due to the magnitude of the intrinsic microwave magnetic field produced by the oscillators. In this context, two HEMT oscillators working at 11 GHz and 25 GHz are realized. In particular, the former achieves the record minimum power consumption (90 uW at 300 K and 4 uW below 30 K) currently reported in the literature for oscillators working in the same frequency range. Also, the proposed sensor achieves a minimum microwave magnetic field of less than 1 uT at 300 K and less than 0.1 uT below 30 K, i.e., orders of magnitude below the values achieved with previous CMOS detectors. Furthermore, an analytical model is carried out in order to estimate the minimum achievable power consumption for an LC single-ended Colpitts oscillator based on any single FET. Lastly, the DC characterization of a standing alone HEMT transistor is provided from 300 K down to 1.4 K, ranging from the standard Ids-Vs-Vds curves to the extraction of both the number of carriers and their effective mobility. The former comes from the analysis of the Shubnikov-de-Haas oscillations whereas the latter is calculated by means of Hall-effect based experiments.

EPFL2019

Single-chip electron spin resonance detectors operating at 50 GHz, 92 GHz, and 146 GHz

Jens Anders, Giovanni Boero, Jürgen Brugger, Gabriele Gualco, Alessandro Valentino Matheoud, Henrik Moodysson Rønnow, Ivica Zivkovic

We report on the design and characterization of single-chip electron spin resonance (ESR) detectors operating at 50 GHz, 92 GHz, and 146 GHz. The core of the single-chip ESR detectors is an integrated LC-oscillator, formed by a single turn aluminum planar coil, a metal-oxide-metal capacitor, and two metal-oxide semiconductor field effect transistors used as negative resistance network. On the same chip, a second, nominally identical, LC-oscillator together with a mixer and an output buffer are also integrated. Thanks to the slightly asymmetric capacitance of the mixer inputs, a signal at a few hundreds of MHz is obtained at the output of the mixer. The mixer is used for frequency down-conversion, with the aim to obtain an output signal at a frequency easily manageable off-chip. The coil diameters are 120 μm, 70 μm, and 45 μm for the U-band, W-band, and the D-band oscillators, respectively. The experimental frequency noises at 100 kHz offset from the carrier are 90 Hz/Hz1/2, 300 Hz/Hz1/2, and 700 Hz/Hz1/2 at 300 K, respectively. The ESR spectra are obtained by measuring the frequency variations of the single-chip oscillators as a function of the applied magnetic field. The experimental spin sensitivities, as measured with a sample of α,γ-bisdiphenylene-β-phenylallyl (BDPA)/benzene complex, are 1 × 108 spins/Hz1/2, 4 × 107 spins/Hz1/2, 2 × 107 spins/Hz1/2 at 300 K, respectively. We also show the possibility to perform experiments up to 360 GHz by means of the higher harmonics in the microwave field produced by the integrated single-chip LC-oscillators.

Academic Press Inc Elsevier Science2017

Methods and microfabrication techniques for subnanoliter magnetic resonance spectroscopy

Enrica Montinaro

Nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) spectroscopy can open up the possibility of studying many scientifically and biologically relevant samples at the µm and sub-µm scale. Examples of volume-limited systems include numerous species of microorganisms, mammalian zygotes, the majority of cells, proteins limited in growth, micro and nanostructured devices for the analysis of spin dynamics at the sub-µm scale. These volume-limited samples cannot be addressed by commercially available inductive spectrometers due to their constraint in sensitivity. It was previously proposed in our group that CMOS technology can be used to realize miniaturized high sensitivity inductive detection systems, having spin sensitivities at least two orders of magnitude greater than the commercially available spectrometers. During my PhD work, I developed methods and microfabrication techniques to perform NMR, EPR and FMR spectroscopy at the µm and sub-µm scale by using high sensitivity single chip CMOS detectors, previously proposed in our group. Microfluidic systems for the non-invasive handling of liquid samples and biological entities immersed in liquids are realized and integrated with the CMOS single chip NMR and EPR detectors. Microfluidic channels are fabricated via conventional microfabrication techniques and via two-photon polymerization, a 3D printing technique with a lateral resolution of 300 nm. The 3D printing technique is found to be an exceptional solution for NMR applications. Due to the flexibility in the design of the microfluidic systems, it is possible to reduce the magnetic field non-uniformieties with a consequent improval in spectral resolution. Spectral resolutions down to 0.007 ppm are reported for liquids having sample volumes of 100 pL. For the first time, NMR studies on intact biological entities submerged in liquid media of choice are performed, using 3D printed microfluidic systems. A spin sensitivity of 2.5·1013 spins/¿Hz is shown, sufficient to detect highly concentrated endogenous compounds in active volumes down to 100 pL with measurement times down to 3 h. EPR measurements on subnanoliter liquids and frozen solutions are reported, by the combination of commercially available capillaries and EPR single chip detectors. This is a first but important step towards the study of biological samples, whose paramagnetic ions have relaxation times too short to be measured at room temperature. Moreover, a novel method for the sensing of magnetic microbeads is presented, which is based on the detection of the change of susceptibility in FMR condition by the CMOS integrated detector. Due to the frequency and field dependence of the susceptibility, the detected variation is 20 times greater than the change in magnetization measured in static conditions by other approaches. The proposed detection scheme allows for single bead sensitivity over an active area of about 5·104 µm2. Lastly, sub-µm scale FMR detection capabilities of the single chip CMOS detector are shown by experiments on nanopatterned single permalloy (80% Ni - 20% Fe) and YIG (Yittrium Iron Garnet) dots. The combination of high sensitivity and large active area is seen as a considerable advantage with respect to other FMR detection methods, which suffer either from sensitivity or from reduced active area.