Concepts and issues in piezo‐on‐3D silicon structures

The purpose of this paper is to explore concepts and manufacturing issues for the emerging piezo on silicon technology being used in ultra‐sound devices. Development of 3D silicon‐on‐silicon structures is now under way. Additional functionality can be achieved using piezoelectric‐on‐silicon structures and work in this area has started. A commercialisation road map is required, specifying development of the design and fabrication techniques from research to high volume and lower volume high‐value manufacture of niche products.

This conceptual paper outlines processes needed, along with their possible sources with illustrations of present capabilities. Included are surface finishing techniques such as grinding, bonding technology for dissimilar materials, and through‐wafer‐via fabrication. Control of acoustic propagation, thermal expansion and electric field fringing effects will be considered.

Areas that require research and development are identified with possible starting points using techniques already used in other applications. Strong emphasis on empirical research highlights possible issues with examples including surface finishing and wafer dicing to show current methods.

Archetypal pixellated piezoelectric‐on‐silicon structures highlight critical points. In the authors' work, such pixellated structures occur in 1‐3 connectivity piezoelectric ceramic‐polymer composites with unit cell length scales from several millimetres, manufactured with mechanical dicing, to less than 50 μm, manufactured with micro‐moulding.

A forward looking approach of “thinking freely” is taken, this opens up potential manufacturing routes and ideas precluded from an iterative approach.

The conclusion suggests the criteria for a “design for” approach linked to either bottom up or top down assembly techniques for the integration of conventional and unusual piezoelectric materials with silicon in 3D structures.