[2022] Lossless integration of 2D arrays of piezoelectric transducers in CMOS technology (Taken)

Ultrasound neuromodulation is an emerging neuronal stimulation modality that combines high spatial resolution with high depth of penetration in neuronal tissue [1]. Two-dimensional (2D) phased arrays are required to create electronically steerable focused ultrasound pressure spots capable of stimulating neuronal circuits in pre-determined locations. The direct integration of a 2D array of piezoelectric ultrasound transducers, that is, directly on top of a CMOS chip, is essential to achieve such a phased array design of any considerable size, due to the high density of interconnections required. Close integration also allows parasitic capacitances between electronics and transducers to be reduced substantially.

One of the major challenge in integrating piezoelectric ultrasound transducers into tiny electronic chips [2,3] is on how to achieve high-enough acoustic intensities at the focal spot from such miniaturized devices. A key factor in maximizing the focal spot acoustic intensity relies on minimizing the losses that occur at the interaction between piezoelectric materials and the CMOS silicon substrate. These losses lead to attenuation in the intensity of the generated acoustic waves, which in turn lead to higher driving voltages, and hence, higher power consumption.

This projects targets the design, fabrication and experimental validation of lossless methods for integrating piezoelectric transducers with silicon substrates.

References:

1. Tufail, Y. et al. Transcranial pulsed ultrasound stimulates intact brain circuits. Neuron 66, 681–94 (2010).

2. Shi, C., Costa, T., Elloian, J. & Shepard, K. L., “Monolithic Integration of Micron-scale Piezoelectric Materials with CMOS for Biomedical Applications“ in 2018 IEEE International Electron Devices Meeting (IEDM). 

3. T. Costa, C. Shi, K. Tien, J. Elloian, F. A. Cardoso, and K. Shepard, "An Integrated 2D Ultrasound Phased Array Transmitter in CMOS with Pixel Pitch-Matched Beamforming," IEEE Transactions on Biomedical Circuits and Systems, vol. 15, no. 4, pp. 731-742, 2021

Assignment

1^st part:  Literature review of ultrasound transducers backing & matching layers.

2^nd part: Design, fabrication and testing of lossless methods for integrating piezoelectric transducers with silicon substrates

Requirements

MSc students from Microelectronics, Biomedical Engineering or Mechanical Engineering. Interested students should include their CV, the list of courses attended, and a motivation letter.

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Last modified: 2022-10-07