Future integration of silicon electronics with miniature piezoelectric ultrasonic transducers and arrays

The long-established pace of progress in semiconductor electronics, expressed by Moore's Law, has led to new opportunities in medical ultrasound imaging. Traditionally, ultrasound systems have separated the transducer array from most of the electronic instrumentation, with multicore physical cabling in between. This avoids problems with electrical power, functional density, and communication bandwidth. However, it is far from ideal in terms of cost, ergonomics, and the need to interface instrumentation and the transducer with the cable, and it causes particular difficulties with miniature devices. Given these issues, and the relatively slow progress in front-end transducer technology, integration of the transducer with electronics is certain to increase, most likely at a pace governed by financial investment, development of electronics for other applications, and the realisation of high volume ultrasound applications. This paper therefore considers motivations for increased integration, technical barriers, and relevant new techniques, particularly related to microelectromechanical systems (MEMS). Increased integration will rely on advances in integrated circuit (IC) electronics, device assembly, and microsystems engineering, with key constraints being the packaging of a system in a small volume and the power supply. System partitioning will determine where functionality will reside physically within the imaging hardware and software. This paper considers relevant recent developments in academic research and industry, with a particular focus on medical applications. IC design is important because it defines parameters such as power consumption. 45 nm ICs are now in high volume production but the present relatively small ultrasound market makes adoption difficult. Ingenuity in exploiting existing technology cost-effectively and bespoke engineering where required are likely to be important for integration of piezoelectric material with electronics technology and functionality will correspond with different layers in a device. In this paper, examples are selected from the authors' work to illustrate progress and suggest how MEMS roadmaps and application demands may relate to future systems.