{"id":1527,"date":"2013-07-25T18:29:23","date_gmt":"2013-07-25T18:29:23","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1527"},"modified":"2013-08-30T15:09:35","modified_gmt":"2013-08-30T15:09:35","slug":"thin-film-piezoelectric-micro-machined-ultrasonic-transducer-for-medical-imaging","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/thin-film-piezoelectric-micro-machined-ultrasonic-transducer-for-medical-imaging\/","title":{"rendered":"Thin Film Piezoelectric Micro-machined Ultrasonic Transducer for Medical Imaging"},"content":{"rendered":"

Ultrasound is an attractive 3D medical imaging technique because it is relatively inexpensive, portable, compact, and non-invasive. However, for 3D real time imaging to be commercially realizable, scans must be consistent and high resolution and occur at a fast acquisition rate–all factors that are inhibited by the current bulk piezoelectric transducer technology[1<\/a>]<\/sup>.\u00a0 Highly manual manufacturing limits the size of current transducers to millimeter length scales and the high acoustic impedance of the bulk piezoelectric limits resolution reducing bandwidth and sensitivity[2<\/a>]<\/sup>.\u00a0 At high volume, micro-fabrication is high yield and less expensive, and it would enable element miniaturization for high resolution, small form factor ultrasound probes.<\/p>\n

Our group has designed a piezoelectric micro-machined ultrasonic transducer (pMUT) that transmits acoustic signals via high frequency vibrations of a thin diaphragm.\u00a0 These vibrations are actuated by applying a voltage across a thin film piezoelectric lead zirconate titanate (PZT) film deposited via a sol-gel technique.\u00a0 For sensing, acoustic waves reflected from an imaging target strain the diaphragm generating a current signal.<\/p>\n

Device fabrication begins with growth of thermal oxide on a silicon-on-insulator wafer.\u00a0 The bottom electrode is then deposited via a lift-off process, and PZT is deposited and patterned with a wet etch.\u00a0 The lift-off process is then repeated to create the top electrode.\u00a0 Finally, diaphragms are released and the substrate is divided into chips (Figure 2) with a back-side deep reactive ion etch.\u00a0 A schematic of the fabricated device is shown in Figure 1.<\/p>\n

Through electrode size optimization, our pMUT is designed to maximize deflection, which is ideal for generating the high acoustic pressure necessary to overcome signal attenuation in deep penetration imaging[3<\/a>]<\/sup>.\u00a0 In the future, we hope to incorporate the optimized pMUT transducer design in pMUT arrays with a small form factor to enable 3D real time medical imaging.<\/p>\n\n\t\t