Electronic Instrumentation Laboratory
Department of Microelectronics

Karen Dowling

Publications

  1. Near-constant thermoelectric power factor of GaN two-dimensional hole gas in cryogenic environments
    Pardon, Lex; Leitao, Diana C.; Cardoso, Filipe A.; Dowling, Karen M.;
    Applied Physics Letters,
    Volume 128, Issue 20, pp. 202107, 05 2026. DOI: 10.1063/5.0324609
    Abstract: ... This work investigates the thermoelectric properties of a gallium nitride (GaN)-based two-dimensional hole gas (2DHG) using a double heterojunction, which can be utilized in complementary GaN thermoelectric (TE) platforms for power generation in extreme environments. A 5×1012 cm−2 hole density, a Hall mobility of up to 20 cm2 V−1 s−1, and a Seebeck coefficient of 0.4 mV K−1 have been measured, resulting in a power factor of 0.5–1.0 mW m−1 K−2 over a 300–77 K temperature range. These results demonstrate the stability and usability of the thermoelectric properties of GaN using hole conduction at sub-100 K temperatures, therefore providing clear evidence that GaN-based 2DHGs can function as a stable cryogenic TE platform, opening new opportunities for complementary device architectures (leveraging both 2DHGs for p-type and two-dimensional electron gases for n-type) optimized for extreme environment electronics commonly encountered in deep-space missions, where other materials become unreliable.

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  2. Inverted Pyramid 3-axis Silicon Hall Effect Magnetic Sensor With Offset Cancellation
    Jacopo Ruggeri; Udo Ausserlechner; Helmut Köck; Karen Dowling;
    Microsystems & Nanonengineering,
    Jan 2025.
    Abstract: ... Microelectronic magnetic sensors are essential in diverse applications, including automotive, industrial, and consumer electronics. Hall-effect devices hold the largest share of the magnetic sensor market, and they are particularly valued for their reliability, low cost and CMOS compatibility. This paper introduces a novel 3-axis Hall-effect sensor element based on an inverted pyramid structure, realized by leveraging MEMS micromachining and CMOS processing. The devices are manufactured by etching the pyramid openings with TMAH and implanting the sloped walls with n-dopants to define the active area. Through the use of various bias-sense detection modes, the device is able to detect both in-plane and out-of-plane magnetic fields within a single compact structure. In addition, the offset can be significantly reduced by one to three orders of magnitude by employing the current-spinning method. The device presented in this work demonstrated high in-plane and out-of-plane current- and voltage-related sensitivities ranging between 64.1 to 198 V A^−1 T^−1 and 14.8 to 21.4 mV V^−1 T^−1, with crosstalk below 4.7 %. The sensor exhibits a thermal noise floor which corresponds to approximately 0.5 μV√Hz at 1.31 V supply. This novel Hall-effect sensor represents a promising and simpler alternative to existing state-of-the-art 3-axis magnetic sensors, offering a viable solution for precise and reliable magnetic field sensing in various applications such as position feedback and power monitoring.

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