Design and development of a reduced form-factor high accuracy three-axis teslameter

Acknowledgments: The authors would like to thank Reuben Debono for his useful guidance and help in the PCB assembly of the instruments at the Electronic Systems Lab at the Faculty of Engineering at University of Malta. The authors would like to thank R. Ganter, project leader of the Athos undulator beamline and H-H. Braun, SwissFEL machine director, for their constant support throughout the entire project. The authors would like to thank Sasa Spasic and his team at Sentronis facilities for their fruitful discussions and their guidance during testing.A novel three-axis teslameter and other similar machines have been designed and developed for SwissFEL at the Paul Scherrer Institute (PSI). The developed instrument will be used for high fidelity characterisation and optimisation of the undulators for the ATHOS soft X-ray beamline. The teslameter incorporates analogue signal conditioning for the three-axes interface to a SENIS Hall probe, an interface to a Heidenhain linear absolute encoder and an on-board high-resolution 24-bit analogue-to-digital conversion. This is in contrast to the old instrumentation setup used, which only comprises the analogue circuitry with digitization being done externally to the instrument. The new instrument fits in a volumetric space of 150 mm × 50 mm × 45 mm, being very compact in size and also compatible with the in-vacuum undulators. This paper describes the design and the development of the different components of the teslameter. Performance results are presented that demonstrate offset fluctuation and drift (0.1–10 Hz) with a standard deviation of 0.78 µT and a broadband noise (10–500 Hz) of 2.05 µT with an acquisition frequency of 2 kHz.peer-reviewe

Calibration and characterization of a reduced form-factor high accuracy three-axis teslameter

A new reduced form-factor three axes digital teslameter, based on the spinning current technique, has been developed. This instrument will be used to characterize the SwissFEL insertion devices at the Paul Scherrer Institute (PSI) for the ATHOS soft X-ray beamline. A detailed and standardized calibration procedure is critical to optimize the performance of this precision instrument. This paper presents the measurement techniques used for the corrective improvements implemented through non-linearity, temperature offset, temperature sensitivity compensation of the Hall probe and electronics temperature compensation. A detailed quantitative analysis of the reduction in errors on the application of each step of the calibration is presented. The percentage peak error reduction attained through calibration of the instrument for reference fields in the range of ±2 T is registered to drop from 1.94% down to 0.02%.peer-reviewe

Polymer-based cantilevers with integrated electrodes

An innovative release method of polymer cantilevers with embedded integrated metal electrodes is presented. The fabrication is based on the lithographic patterning of the electrode layout on a wafer surface, covered by two layers of SU-8 polymer: a 10-um-thick photo-structured layer for the cantilever, and a 200-um-thick layer for the chip body. The releasing method is based on dry etching of a 2-um-thick sacrificial polysilicon layer. Devices with complex electrode layout embedded in free-standing 500-um-long and 100-um-wide SU-8 cantilever were fabricated and tested.We have optimized major fabrication steps such as the optimization of the SU-8 chip geometry for reduced residual stress and for enhanced underetching, and by defining multiple metal layers [titanium (Ti), aluminum (Al), bismuth (Bi)] for improved adhesion between metallic electrodes and polymer. The process was validated for a miniature 2x2 um2 Hall-sensor integrated at the apex of a polymer microcantilever for scanning magnetic field sensing. The cantilever has a spring constant of =1 N/m and a resonance frequency of=17 kHz. Galvanometric characterization of the Hall sensor showed an input/output resistance of 200 ohm, a device sensitivity of 0.05 V/AT and a minimum detectable magnetic flux density of 9 uT/Hz^1/2 at frequencies above 1 kHz at room temperature. Quantitative magnetic field measurements of a microcoil were performed. The generic method allows for a stable integration of electrodes into polymers MEMS and it can readily be used for other types of microsensors where conducting metal electrodes are integrated in cantilevers for advanced scanning probe sensing applications.LMIS3LMIS

CMOS imager based on single photon avalanche diodes

In this paper we report on a 32×32 optical imager based on single photon avalanche diodes integrated in CMOS technology. The maximum measured dynamic range is 120dB and the minimum noise equivalent intensity is 1.3×-3lx. The minimum integration time per pixel is 4μs. The output of each pixel is digital, thereby requiring no complex read-out circuitry, no amplification, no sample & hold, and no ADC

Current and voltage ADC using a differential pair of single-electron bipolar avalanche transistors

Single-electron bipolar avalanche transistors (SEBATs) enable current sensing by electron counting at room temperature. Here, differential SEBAT circuits combining the functions of amplification and analog-to-digital (A/D) conversion are proposed and characterized for two applications: Low-current AID conversion and differential voltage A/D conversion. Charge detection efficiencies in the order of 30% are reached, allowing for the direct A/D conversion of currents in the 10(-13) A range. An equivalent of the differential pair is used as a differential voltage ADC

Accurate 3-axis measurement of inhomogeneous magnetic fields

Hall effect based Teslameters/Gaussmeters measure DC and AC magnetic flux densities in the range from a few mu T to about 30 T. For accurate measurement a 3-axis Hall probe is applied with small magnetic field sensitive volume (MFSV) of 100 mu m x 10 mu m x 100 mu m, with vertical and horizontal Hall elements integrated on a single chip. The planar Hall effect, that produces additional measurement errors is suppressed by the spinning current technique. The orthogonality error of the 3-axis Hall probe is reduced to smaller than 0.1 degrees by the described calibration procedure. This paper explains why the above features are crucial for some applications in industry and modern science for accurate measurement of inhomogeneous magnetic fields and how to achieve them. The future technology trends in magnetic metrology are introduced and the newly developed Nanomapper that incorporates a 3-axis Hall probe with a MFSV of smaller than 10 x 10 x 10 micrometer is presented

On performance of series connected CMOS vertical hall devices

Series connected (stacked) CMOS vertical Hall devices were analyzed on the basis of performance of a single five contacts device biased at different common mode voltages with respect to the substrate. The uneven influence of junction field effect on residual offset voltage, sensitivity and residual offset equivalent magnetic field was studied. It was shown that though junction field effect leads to some increase in offset voltage for devices with higher common mode, this effect can be minimized through suitable biasing

Ultra Low-Power Angular Position Sensor for High-Speed Portable Applications

We present a technique for contactless angular position sensing that allows low power consumption while keeping dynamic properties comparable to existing sensors. The technique essentially consists in combining a recently developed sensing element, the so-called Circular Vertical Hall Device, with a simple and robust signal treatment based on phase detection. Because of its low startup time, this circuit is specially suited for pulsed mode operation, which enables to further decrease the power consumption. More generally, the absence of complex digital signal treatment makes this technique a natural method for measuring the magnetic field direction and therefore for designing an angular position sensor using Hall probes

Purely CMOS Angular Position Sensor Based on a New Hall Microchip

This paper presents a new technique to sense the direction of the magnetic field, enabling a new generation of contactless 360 degrees absolute angle encoders. The sensor consists of a microchip that contains a special ring-shaped Hall element. It is the first sensor that gives the angle value without the need of computing an arctan function. In addition, we demonstrate that this system is compatible with a self calibration method. Measurements were performed with the microchip operating inside a hollow permanent magnet and an accuracy of 0.1 degrees was obtained without calibration