Ultrasonic transducers are used in a multitude of fields. In particular, they are used in almost all fields of medicine such as cardiology, ophthalmology, orthopedics, for cancer screening, for prenatal tests to name a few. Their use is also widespread in several industrial fields such as the metallurgical industry for quality control and detection of hidden cracks and internal irregularities. Finally, they are also used for motion detection and distance measurements.
Despite their omnipresence, ultrasonic transducers are still very bulky, expensive and ineffective. A new type of transducer, the micromachined piezoelectric ultrasonic transducer (PMUT) is currently attracting a lot of interest. PMUTs are manufactured using microfabrication techniques from MEMS and semiconductor technologies and can therefore be mass-produced at low cost.
The objective of this thesis is to investigate the possibility of creating a miniature ultrasonic chip, at low cost and easy to integrate. The chip will consist of a matrix of PMUT and an integrated circuit for controlling the transducers.
First, a new low-cost technique for adjusting the resonance frequency of PMUTs is explored. The influence of process variations on the resonant frequency raises the need to develop an adjustment method that is simple and inexpensive. The proposed technique requires only a single post-treatment step which consists of depositing a thin layer of Parylene-C. The thickness of the layer can be precisely controlled and allows custom adjustment of the resonant frequency.
Then, a new PMUT architecture allowing a drastic reduction of the impact of process variations on the resonance frequency is presented. Briefly, the effectiveness of this topology is based on an innovative toroidal anchoring technique. The measurement results show that the variation in the resonance frequency of PMUTs due to process variations can be reduced by a factor of approximately 4. The manufactured PMUTs are used to perform distance measurements.
Next, a new technique for damping PMUT is presented. The objective of this technique is to decrease the length of the pulses in the time domain and thus increase the image resolution that one could obtain. The proposed PMUT is surrounded by two mechanical dampers. These can be moved using electrostatic actuators to put them in contact with the PMUT. The measurement results show that this technique can effectively dampen the displacement of a PMUT.
Finally, a system in package (SiP) for ultrasonic applications composed of a 4x8 matrix of PMUT and an integrated CMOS interface circuit is presented. The CMOS circuit is mainly used to attack PMUT to generate acoustic pulses and to amplify the return echo. In order to demonstrate its operation, the system is used to perform distance measurements.
| Date | 8 Sept 2020 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Frédéric Nabki (Supervisor) & Dominic Deslandes (Co-supervisor) |
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Robichaud, A. (Author),
Nabki (Supervisor) &
Deslandes (Co-supervisor),
8 Sept 2020Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering