A hardwired machine learning processing engine fabricated with submicron metal-oxide thin-film transistors on a flexible substrate

Abstract

Flexible electronics can create lightweight, conformable components that could be integrated into smart systems for applications in healthcare, wearable devices and the Internet of Things. Such integrated smart systems will require a flexible processing engine to address their computational needs. However, the flexible processors demonstrated so far are typically fabricated using low-temperature poly-silicon thin-film transistor (TFT) technology, which has a high manufacturing cost, and the processors that have been created with low-cost metal-oxide TFT technology have limited computational capabilities. Here, we report a processing engine that is fabricated with a commercial 0.8-μm metal-oxide TFT technology. We develop a resource-efficient machine learning algorithm (the ‘univariate Bayes feature voting classifier’) and demonstrate its implementation with hardwired parameters as a flexible processing engine for an odour recognition application. Our flexible processing engine contains around 1,000 logic gates and has a gate density per area that is 20–45 times higher than other digital integrated circuits built with metal-oxide TFTs.

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Fig. 1: OFET sensors and system architecture of the flexible smart system.
Fig. 2: Design space exploration with various ML algorithms.
Fig. 3: The UB-FVC.
Fig. 4: Implementation of the UB-FVC as a natively flexible processing engine.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The code used to generate the plots within this paper is available from the corresponding author upon reasonable request.

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Acknowledgements

This work is partially supported by Innovate UK through the ‘PlasticARMPit: Accelerating the Development of Flexible Integrated Smart Systems (no. 103390)’ project.

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Contributions

E.O. and G.B. conceived the UB-FVC model. E.O., J.K. and J.B. designed and implemented the model as an NFPE. A.R., A.S., C.R. and S.W. developed the fabrication process and methodology for the NFPE. All authors contributed to analysis of the data generated in the design, implementation and fabrication of the NFPE. E.O., J.K., J.M., J.B., C.R. and S.W. wrote the paper.

Corresponding author

Correspondence to Emre Ozer.

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Extended data

Extended Data Fig. 1 Transfer characteristics.

Forward transfer characteristic of a metal-oxide TFT.

Extended Data Fig. 2 NFPE simulation results.

The column on the left shows the list of input, intermediate and output signals. Sensor[4:0] and Address[2:0] are the inputs, and represent the 5-bit sensor data, and 3-bit sensor address, respectively. SensorX_vote[4:0] is intermediate signals, and represent the 5-bit BC coefficients (essentially votes) for each sensor. Finally, Output[4:0] shows the 5-bit one-hot predicted class as output.

Extended Data Fig. 3 One-hot coefficients to represent BCs.

The top row shows the sensor data values from 0 to 31. For each sensor value, the BC or vote of the sensor is predetermined and hardwired in the microarchitecture.

Extended Data Fig. 4 NFPE chip measurement results of a fabricated chip for the same set-up as in the simulation.

This is the waveform captured from the logic analyser. All inputs and outputs are shown as individual signals. Sensor_X and Address_X are input signals, and represent the 5-bit sensor data and 3-bit address. Output_X represents the 5-bit one-hot predicted class output signals.

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Ozer, E., Kufel, J., Myers, J. et al. A hardwired machine learning processing engine fabricated with submicron metal-oxide thin-film transistors on a flexible substrate. Nat Electron 3, 419–425 (2020). https://doi.org/10.1038/s41928-020-0437-5

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