Ultra-Low Power Circuits for Batteryless Energy Harvesting Systems and Thermal Compensation in Resistive In-Memory Computing

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2025-08-29
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Authors

Date

2025

Department

Elektroniikan ja nanotekniikan laitos
Department of Electronics and Nanoengineering

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Mcode

Degree programme

Language

en

Pages

105 + app. 104

Series

Aalto University publication series Doctoral Theses, 145/2025

Abstract

Embedded systems, from wearable health monitors and implantable diagnostics to environmental sensor nodes, are becoming increasingly prevalent in modern life. These platforms are often expected to operate continuously under severe energy constraints, where frequent battery replacement is impractical. To address this, there is a growing need for ultra-low-power (ULP) circuits capable of harvesting ambient energy from sources such as radio frequency (RF) fields, biochemical reactions, and photovoltaic cells. Ensuring stable operation under these limited and varying energy conditions requires circuits with ULP consumption and robust performance under variations. This thesis presents an approach to the design, implementation, and experimental validation of ULP integrated circuits across multiple circuit blocks, tailored for energy-autonomous and flexible systems. The contributions span several key building blocks of energy-harvesting systems, including variation-insensitive voltage and current reference generators, RF-DC converters, low-dropout (LDO) regulators, and switched-capacitor (SC) DC-DC converters with finegrained, arithmetic progression-based voltage scaling. Further, the work introduces thermal compensation techniques to maintain computational accuracy for analog in-memory computing units under varying thermal conditions. The circuits presented in this thesis are designed and fabricated using a conventional CMOS in 65 nm and Pragmatic 600 nm flexible indium gallium zinc oxide (IGZO) based technology using unipolar TFT-based transistors. Variation-insensitive reference generators form the foundation for reliable biasing across the circuits presented in this work. To address this, the thesis implements amplifier-free, MOS-based voltage and current references that ensure stable operation under varying conditions. A dual-mode, all-NMOS circuit is developed to function both as a voltage reference and a temperature sensor, enabling efficient circuit reuse in energy and area constrained systems. This circuit is further extended to flexible electronics, with a voltage reference designed using IGZO thin-film transistors. For energy regulation, an LDO based on IGZO unipolar transistors is presented, offering efficient voltage regulation under a low quiescent current of 150 nA. An RF-to-DC converter targeting operation in 13.56 MHz is also developed to harvest energy from wireless sources. To support energy sources with variable and degrading outputs, such as biofuel or zinc-air cells, a reconfigurable switched-capacitor DC-DC converter is introduced, with arithmetic progression control of voltage conversion steps of 0.125. The proposed circuits are implemented for voided fluid volume sensing in smart diapers powered by urine-based energy harvesters. Additionally, voltage regulation using DC-DC converters operating from degrading and decaying energy sources has been designed. The circuits implemented are validated through system-level integration in practical applications. A smart diaper platform powered entirely by harvested urine energy demonstrates the feasibility of fully autonomous operation. Additionally, the thesis addresses thermal variability in analog in-memory computing arrays through two compensation techniques: one using programmable calibration, and another using on-chip thermal sensing for automatic adjustment. The circuits developed in this work enable energy-autonomous operation in batteryless systems and provide robust thermal stability for analog in-memory computing.

Description

Supervising professor

Halonen, Kari, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland

Thesis advisor

Halonen, Kari, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland

Keywords

energy harvesting, in-memory computing, power management, ultra-low-power

Other note

Parts

  • [Publication 1]: D. C. Monga and K. Halonen. An Arithmetic VCR DC-DC Converter for IoT Nodes Powered by Decaying and Degrading Energy Sources. (Submitted), pp. 1–13, July 2025.
  • [Publication 2]: M. Tanweer*, D. C. Monga*, Gaurav Singh, Liam Gillan, Raimo Sepponen, Ihsan Oguz Tanzer, Kari A. Halonen. Urine-Powered Batteryless Sensor Node with Printed Harvesters and Sensors for Smart Diapers. IEEE Internet of Things Journal, pp. 1–13, May 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202508085837
    DOI: 10.1109/JIOT.2025.3573459 View at publisher
  • [Publication 3]: M. Tanweer*, D. C. Monga*, L. Gillan, R. Sepponen, I. O. Tanzer and K. A. I. Halonen. Smart Diaper with Printed Capacitive Sensors and Integrated Front-End to Monitor Voided Fluid Volume. IEEE Sensors Journal, vol. 24, no. 9, pp. 14443–14453, May 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202405293988
    DOI: 10.1109/JSEN.2024.3380890 View at publisher
  • [Publication 4]: D. C. Monga and K. Halonen. Ultra-low Quiescent Current, Unipolar TFT-based Low Dropout Regulator on Flexible Substrate for Biomedical Implants. (Submitted), pp. 1–4, May 2025.
  • [Publication 5]: D. C. Monga and K. Halonen. Flexible RF to DC Converter for Wireless Power Transfer in NFC and Biomedical Systems. In 2024 IEEE International Conference on Flexible and Printable Sensors and Systems (FLEPS), Tampere, Finland, pp. 1–4, July 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202409186404
    DOI: 10.1109/FLEPS61194.2024.10603873 View at publisher
  • [Publication 6]: D. C. Monga and K. Halonen. A Dual Mode All NMOS 7-T Temperature Sensor and Voltage Reference for Biomedical Applications. In 2024 IEEE International Symposium on Circuits and Systems (ISCAS), Singapore, Singapore, pp. 1–5, May 2024.
    DOI: 10.1109/ISCAS58744.2024.10558329 View at publisher
  • [Publication 7]: D. C. Monga and K. Halonen. A Sub-nW Temperature Invariant Voltage Reference in a Unipolar TFT-based Flexible IC Technology. In 2024 IEEE International Conference on Flexible and Printable Sensors and Systems (FLEPS), Tampere, Finland, pp. 1–4, July 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202409186388
    DOI: 10.1109/FLEPS61194.2024.10603932 View at publisher
  • [Publication 8]: D. C. Monga and K. Halonen. A Compact Untrimmed 48ppm/°C All MOS Current Reference Circuit. In 2022 IEEE 65th International Midwest Symposium on Circuits and Systems (MWSCAS), Fukuoka, Japan, pp. 1–5, August 2022.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202210195952
    DOI: 10.1109/MWSCAS54063.2022.9859347 View at publisher
  • [Publication 9]: D. C. Monga*, G. Singh*, O. Numan, K. Adam, M. Andraud, and K. A. Halonen. TRIM: Thermal auto-compensation for resistive in-memory computing. IEEE Transactions on Computer-Aided Design Integrated Circuits and Systems, pp. 1–12, July 2025.
  • [Publication 10]: D. C. Monga, O. Numan, M. Andraud and K. Halonen. A temperature and process compensation circuit for resistive-based in-memory computing arrays. In 2023 IEEE International Symposium on Circuits and Systems (ISCAS), Monterey, CA, USA pp. 1–5, May 2023.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202308305337
    DOI: 10.1109/ISCAS46773.2023.10181619 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-2659-4

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[diss] Sähkötekniikan korkeakoulu / ELEC