05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Ultra-low-noise readout circuits for magnetoresistive sensors(2023) Mohamed, Ayman; Anders, Jens (Prof. Dr.-Ing.)The continuous search for highly sensitive, agile and cost-effective sensors for magnetic biosensing applications has been met with high performance magnetoresistive (MR) sensors. While the MR effect has been discovered 150 years ago, there is a growing trend of improving the sensitivity of MR sensors while keeping their noise performance as low as possible. However, such improvements have to be complemented with high performance frontends that can effectively amplify the minute MR sensor's signals while keeping the system's noise floor unaltered. More importantly, the designed frontends have to be equipped with offset compensation peripheral circuits that can efficiently handle the large spread of the base resistance in MR sensors with high MR ratios such as in tunnel magnetoresistive (TMR) sensors. In this thesis, we developed multiple frontend electronics that successfully interfaced MR sensors while, simultaneously, achieving competitive noise performance compared to state-of-the-art (SoA) designs tailored for MR sensor readout. The first variant of chips are specically designed for high performance and high linearity designs thanks to a novel implementation of an ultra-low-noise current bias achieving SoA current noise floor of 2.2 pA/sqrt(Hz) and chopped voltage-mode amplification stages resulting in a total voltage noise floor of 8 nV/sqrt(Hz), including a TMR sensor and a reference resistor with base resistance of 1 kOhm. In order to integrate an analog-to-digital converter (ADC) without substantial additional power and/or area, we show in this work a continuous-time current-mode Sigma-Delta modulator (CT C-SDM) that can directly interface MR sensors without additional amplifiers. Our proposed design does not only show a competitive noise floor of 8.1 pA/sqrt(Hz), but also features a novel DC servo loop (DSL) around the modulator that maximizes the useful dynamic range (DR) of the modulator while successfully rejecting the undesired DC offsets of MR sensors. Both design variants shown in this thesis, pave the way to designing high performance point-of-care (PoC) systems for in-vitro diagnostics while keeping their costs low compared to alternative bulky and expensive systems.Item Open Access Electrically detected magnetic resonance on a chip (EDMRoC) for analysis of thin-film silicon photovoltaics(2023) Segantini, Michele; Marcozzi, Gianluca; Djekic, Denis; Chu, Anh; Amkreutz, Daniel; Trinh, Cham Thi; Neubert, Sebastian; Stannowski, Bernd; Jacob, Kerstin; Rudolph, Ivo; McPeak, Joseph E.; Anders, Jens; Naydenov, Boris; Lips, KlausElectrically detected magnetic resonance (EDMR) is a spectroscopic technique that provides information about the physical properties of materials through the detection of variations in conductivity induced by spin-dependent processes. EDMR has been widely applied to investigate thin-film semiconductor materials in which the presence of defects can induce the current limiting processes. Conventional EDMR measurements are performed on samples with a special geometry that allows the use of a typical electron paramagnetic resonance (EPR) resonator. For such measurements, it is of utmost importance that the geometry of the sample under assessment does not influence the results of the experiment. Here, we present a single-board EPR spectrometer using a chip-integrated, voltage-controlled oscillator (VCO) array as a planar microwave source, whose geometry optimally matches that of a standard EDMR sample, and which greatly facilitates electrical interfacing to the device under assessment. The probehead combined an ultrasensitive transimpedance amplifier (TIA) with a twelve-coil array, VCO-based, single-board EPR spectrometer to permit EDMR-on-a-Chip (EDMRoC) investigations. EDMRoC measurements were performed at room temperature on a thin-film hydrogenated amorphous silicon (a-Si:H) pin solar cell under dark and forward bias conditions, and the recombination current driven by the a-Si:H dangling bonds (db) was detected. These experiments serve as a proof of concept for a new generation of small and versatile spectrometers that allow in situ and operando EDMR experiments.Item Open Access Monitoring the state of charge of vanadium redox flow batteries with an EPR-on-a-Chip dipstick sensor(2024) Künstner, Silvio; McPeak, Joseph E.; Chu, Anh; Kern, Michal; Dinse, Klaus-Peter; Naydenov, Boris; Fischer, Peter; Anders, Jens; Lips, KlausThe vanadium redox flow battery (VRFB) is considered a promising candidate for large-scale energy storage in the transition from fossil fuels to renewable energy sources. VRFBs store energy by electrochemical reactions of different electroactive species dissolved in electrolyte solutions. The redox couples of VRFBs are VO2+/VO2+ and V2+/V3+, the ratio of which to the total vanadium content determines the state of charge (SOC). V(iv) and V(ii) are paramagnetic half-integer spin species detectable and quantifiable with electron paramagnetic resonance spectroscopy (EPR). Common commercial EPR spectrometers, however, employ microwave cavity resonators which necessitate the use of large electromagnets, limiting their application to dedicated laboratories. For an SOC monitoring device for VRFBs, a small, cost-effective submersible EPR spectrometer, preferably with a permanent magnet, is desirable. The EPR-on-a-Chip (EPRoC) spectrometer miniaturises the complete EPR spectrometer onto a single microchip by utilising the coil of a voltage-controlled oscillator as both microwave source and detector. It is capable of sweeping the frequency while the magnetic field is held constant enabling the use of small permanent magnets. This drastically reduces the experimental complexity of EPR. Hence, the EPRoC fulfils the requirements for an SOC sensor. We, therefore, evaluate the potential for utilisation of an EPRoC dipstick spectrometer as an operando and continuously online monitor for the SOC of VRFBs. Herein, we present quantitative proof-of-principle submersible EPRoC experiments on variably charged vanadium electrolyte solutions. EPR data obtained with a commercial EPR spectrometer are in good agreement with the EPRoC data.Item Open Access Compact electron paramagnetic resonance on a chip spectrometer using a single sided permanent magnet(2024) Segantini, Michele; Marcozzi, Gianluca; Elrifai, Tarek; Shabratova, Ekaterina; Höflich, Katja; Deaconeasa, Mihaela; Niemann, Volker; Pietig, Rainer; McPeak, Joseph E.; Anders, Jens; Naydenov, Boris; Lips, KlausElectron paramagnetic resonance (EPR) spectroscopy provides information about the physical and chemical properties of materials by detecting paramagnetic states. Conventional EPR measurements are performed in high Q resonator using large electromagnets which limits the available space for operando experiments. Here we present a solution toward a portable EPR sensor based on the combination of the EPR-on-a-Chip (EPRoC) and a single-sided permanent magnet. This device can be placed directly into the sample environment (i.e., catalytic reaction vessels, ultrahigh vacuum deposition chambers, aqueous environments, etc.) to conduct in situ and operando measurements. The EPRoC reported herein is comprised of an array of 14 voltage-controlled oscillator (VCO) coils oscillating at 7 GHz. By using a single grain of crystalline BDPA, EPR measurements at different positions of the magnet with respect to the VCO array were performed. It was possible to create a 2D spatial map of a 1.5 mm × 5 mm region of the magnetic field with 50 μm resolution. This allowed for the determination of the magnetic field intensity and homogeneity, which are found to be 254.69 mT and 700 ppm, respectively. The magnetic field was mapped also along the vertical direction using a thin film a-Si layer. The EPRoC and permanent magnet were combined to form a miniaturized EPR spectrometer to perform experiments on tempol (4-hydroxy-2,2,6,6-teramethylpiperidin-1-oxyl) dissolved in an 80% glycerol and 20% water solution. It was possible to determine the molecular tumbling correlation time and to establish a calibration procedure to quantify the number of spins within the sample.Item Open Access Current trends in VCO-based EPR(2024) Kern, Michal; Chu, Anh; Anders, JensIn this article we provide an overview of chip-integrated voltage-controlled oscillator (VCO)-based EPR detection as a new paradigm in EPR sensing. After a brief motivation for this alternative detection method, we provide a self-contained overview of the detection principle, both for continuous-wave and pulsed detection. Based on this introduction, we will highlight the advantages and disadvantages of VCO-based detection compared to conventional resonator-based detection. This is followed by an overview of the current state of the art in VCO-based EPR and interesting emerging applications of the technology. The paper concludes with a brief summary and outlook on future research directions.Item Open Access Frontend and backend electronics achieving flexibility and scalability for tomographic tactile sensing(2024) Sánchez-Delgado, Alberto; Garg, Keshav; Scherjon, Cor; Lee, HyosangTactile sensing is essential for robots to adequately interact with the physical world, but creating tactile sensors for the robot’s soft and flexible body surface has been a challenge. The resistance tomography-based tactile sensors have been introduced as a promising approach to creating soft tactile skins because the sensor fabrication can be greatly simplified with the aid of a computation model. This article introduces an electronic design strategy dividing frontend and backend electronics for the resistance tomography-based tactile sensors. In this scheme, the frontend is made of the piezoresistive structure and electrodes that can be changed depending on the required geometry. The backend is the electronic circuit for resistance tomography, which can be used for various frontend geometries. To evaluate the use of a unified backend for different frontend geometries, two frontend specimens with a square shape and a circular shape are tested. The minimum detectable contact force and the minimum discernible contact distance are calculated as 0.83×10-4 N/mm 2, 2.51 mm for the square-shaped frontend and 1.19×10-4 N/mm 2, 3.42 mm for the circular-shaped frontend. The results indicated that the proposed electronic design strategy can be used to create tactile skins with different scales and geometries while keeping the same backend design.Item Open Access Dead time-free detection of NMR signals using voltage-controlled oscillators(2023) Kern, Michal; Klotz, Tobias; Spiess, Maximilian; Mavridis, Petros; Blümich, Bernhard; Anders, JensIn this paper, we introduce voltage-controlled oscillators (VCOs) as a new type of nuclear magnetic resonance (NMR) detector, enabling dead time-free detection of NMR signals after an excitation pulse as well as the real-time inductive detection of Rabi oscillations during the pulse. Together with the theory of operation, we present the details of a custom-designed prototype implementation of a VCO-based NMR detector with an operating frequency around 62 MHz. The proof-of-concept measurements obtained with this prototype clearly demonstrate the possibility of performing dead time-free NMR experiments with coherent spin manipulation. Moreover, we also experimentally verified the capability of VCO-based detectors for performing real-time inductive detection of Rabi oscillations during the excitation pulse.Item Open Access Efficient control and readout of electron spins using custom integrated circuits(2025) Lotfi, Hadi; Anders, Jens (Prof. Dr.-Ing.)In recent decades, the precise manipulation and control of electron spin states have become essential in the development of spintronic sensors. This progress is particularly crucial in fields such as electron paramagnetic resonance (EPR) spectroscopy and quantum sensing based on optically detected magnetic resonance (ODMR) techniques. These spintronic techniques, rooted in quantum mechanics, exploit the intrinsic magnetic properties of particles with unpaired electrons to probe their environment, offering excellent room-temperature sensitivity, long-term stability, and potential for calibration-free measurements. In these applications, an external RF/microwave magnetic field can be employed to manipulate the spin states of NV centers in quantum magnetometry or samples with unpaired electrons in EPR spectroscopy. Concurrently, RF integrated circuits (RFICs) have revolutionized a broad range of applications, from wireless communication systems to medical devices and sensing technologies, due to their excellent performance, compactness, efficiency, and cost-effectiveness. Despite these advancements, conventional quantum sensors and EPR spectrometers typically rely on commercial vector signal generators (VSGs) and bulky, rack-based microwave (MW) amplifiers to generate the required microwave magnetic fields for spin manipulation. This traditional approach severely limits the portability, scalability, and affordability of electron spin-based sensors, making them less practical for widespread use. To overcome these limitations, we propose leveraging custom-designed, chip-integrated RF/microwave sources and transceivers. By integrating these components onto a single chip, we can significantly enhance the portability and scalability of quantum sensors and EPR systems. These on-chip solutions can generate the necessary microwave fields via embedded coils in voltage-controlled oscillators (VCOs) or custom-designed transceivers driving on-chip or off-chip resonators. In this study, we propose eight different chip-scale systems realized through the tight integration of electronics, electromagnetics, and qubits/spectroscopy on BiCMOS and GaN technologies. For ODMR-based quantum magnetometry, we present three different TX frontend configurations: a high-performance BiCMOS TX-chip operating in the Sband frequency (zero-field) with a novel custom resonator for large active area NV-based magnetometry, a 4-channel BiCMOS transmitter chip with a quadrature phase-locked loop (QPLL) for wide frequency range C-band applications, and a high-performance GaN technology chip utilizing a novel parallel LC-resonator for efficient on-chip microwave magnetic field generation. Furthermore, we detail the design and fabrication of a novel RF transceiver chip and three high-performance PLL chips using SiGe BiCMOS technology for EPR spectroscopy. These PLL chips incorporate VCOs with varying sensing areas and performance levels to accommodate different EPR experimental requirements. By employing these advanced RFICs, we aim to create more compact, efficient, and scalable solutions for spin-based measurements, paving the way for broader adoption and new applications in both scientific research and industry.Item Open Access Towards an EPR on a chip spectrometer for monitoring radiation damage during X-ray absorption spectroscopy(2024) Shabratova, Ekaterina; Lotfi, Hadi; Sakr, Ayman; Hassan, Mohamed Atef; Kern, Michal; Neeb, Matthias; Grüneberger, René; Klemke, Bastian; Marcozzi, Gianluca; Kiefer, Klaus; Tsarapkin, Aleksei; Höflich, Katja; Dittwald, Alina; Denker, Andrea; Anders, Jens; McPeak, Joseph E.; Lips, KlausElectron paramagnetic resonance (EPR) spectroscopy is an essential tool to investigate the effects of ionizing radiation, which is routinely administered for reducing contaminations and waste in food products and cosmetics as well as for sterilization in industry and medicine. In materials research, EPR methods are not only employed as a spectroscopic method of structural investigations, but also have been employed for detection of changes in electronic structure due to radiation damage from high energy X-rays, for example, to monitor radical formation inside biomolecules caused by X-ray irradiation at carbon, nitrogen, and oxygen K-edges at synchrotron facilities. Here a compact EPR spectrometer, based on EPR-on-a-chip (EPRoC) sensor and a portable electromagnet, has been developed as a solution for monitoring radiation damage of samples during their investigation by X-ray absorption spectroscopy (XAS) at synchrotron facilities. A portable electromagnet with a soft iron core and forced air temperature stabilization was constructed as the source of the external magnetic field. The sweep range of magnetic field inside the most homogeneous region of the portable electromagnet is 12-290 mT. The compact spectrometer performance was evaluated by placing the EPRoC sensor inside either a commercial electromagnet or the portable electromagnet to record the EPR spectrum of tempol, irradiated alanine, and dilithium phthalocyanine (Li2Pc). The potential performance of the portable spectrometer for the detection of radiation damage in organic compounds and transition metal-containing catalysts during XAS measurements in both fluorescence and transmission modes was calculated with promising implications for measurements after implementation in a synchrotron-based XAS spectrometer.Item Open Access Sensing multi-directional forces at superresolution using taxel value isoline theory(2025) Sun, Huanbo; Spiers, Adam; Lee, Hyosang; Fiene, Jonathan; Martius, GeorgRobots can benefit from touch perception for enhanced interaction. Interaction involves tactile sensing devices, contact objects, and complex directional force motions (normal and shear) in between. We introduce a comprehensive theory unifying them to advance sensor design, explain shear-induced performance drops, and suggest application scenarios. Our theory, based on sensor isolines, achieves superresolution sensing with sparse units, avoiding dense layouts. Through structural analysis of the sensor perception field, force sensitivity, and contact object effects, we also explore the force direction influences: normal, tangential shear, and radial shear forces. The model predicts an inherent accuracy reduction under shear forces compared to pure normal forces. Validation used Barodome, a 3D sensor predicting contact locations and decoupling shear/normal forces. Its performance confirmed the significant impact of shear forces, with observed drops (0.5 mm) closely matching theoretical predictions (0.33 mm). This theory provides valuable guidance for future tactile sensor design and advanced robotic touch systems.