The aim of this work was to optimize the shape of the cross-shaped Hall devices with regard to noise generated on sensing contacts.
We have performed systematical experimental and numerical study of the influence of the geometry of the cross shaped Hall devices on the electrical low frequency noise measured on the sensing and driving current contacts. Based on our numerical calculations of the current density distribution (Finite Elements Method) we have designed several samples with various geometry/shape and dimensions in the 10 μm-200 μm range. Hall devices were fabricated on GaAs-based pseudomorphic heterostructures. Presented experimental results are in good agreement with our calculations of the noise power density based on electrical network theory and references therein. These results enable us to optimize the geometry of the devices giving us in the best case the reduction of the low frequency noise power density by ca -10 dB as compared to a standard Greek cross of identical size. This purely geometrical effect is independent of the sample physical structure and depends only on the sample shape. These results can be applied to any planar Si or III-V based semiconductor Hall device.
We report on studies aimed at understanding and improving the intrinsic noise of high-performance sensors using a 2D electron gas channel confined by a quantum well in the pseudomorphic AlGaAs/InGaAs/GaAs heterostructure. MIS gated and ungated Hall sensors shaped as a Greek cross with dimensions ranging from 100 μm down to submicrometer range have been investigated. At room temperature the predominant low frequency Hall voltage noise originates from the ensemble of trapping/detrapping events occurring within the continuum of GaAs surface states. Its power spectral density can be deduced from independent measurements of the interface trap density-of-states by applying Shockley-Read-Hall dynamics and the Fluctuation-Dissipation Theorem. In fact, theoretical spectra calculated without any adjustable fitting parameter coincide closely with the experimentally measured ones. At cryogenic temperature this interface traps noise freezes out, thus revealing a much weaker intrinsic background noise with 1/f spectrum. For small sensors the intrinsic 1/f noise converts into one or a few lorentzians due to the action of individual random telegraph signals (RTS). For Hall crosses with an intersection of 4x4μm2, we find statistically less than 1 fluctuator per each decade of time constant at 77 K. Due to the random distribution of the elementary fluctuators, some of these small Hall crosses may show less low-frequency noise than much larger 60x60μm2 sensors.
Hall sensors are used in a very wide range of applications. A very demanding one is electrical current measurement for metering purposes. In addition to high precision and stability, a sufficiently low noise level is required. Cost reduction through sensor integration with low-voltage/low-power electronics is also desirable. The purpose of this work is to investigate the possible use of SOI (Silicon On Insulator) technology for this integration. We have fabricated SOI Hall devices exploring a wide range of silicon layer thickness and doping level. We show that noise is influenced by the presence of LOCOS and p-n depletion zones near the edges of the active zones of the devices. A proper choice of SOI technological parameters and process flow leads to up to 18 dB reduction in Hall sensor noise level. This result can be extended to many categories of devices fabricated using SOI technology.