Ultrasonics in integrated electronics

The capabilities of present integrated circuits are limited since only electrical interactions in solids are being utilized. The point of view is presented that additional degrees of freedom will be obtained in the future through the use of "Functional" electronic devices which also utilize mechanical, thermal, radiation, and/or magnetic phenomena. Development of these functional devices will come in response to pressure to overcome specific limitations imposed by present technology. In particular, no satisfactory substitute for an inductor is presently available in integrated electronics technology. The most serious limitation which results is the inability to achieve a narrow band-pass frequency response, a limitation which hinders the full exploitation of present capabilities in a wide variety of systems. Electromechanical resonators offer an extremely promising solution to this "tuning problem" because of their inherent compatibility of size and stability of Q and resonant frequency. Progress to date on integratable mechanically resonant devices covering the frequency range from less than 1 kc/s to more than 100 Mc/s is reviewed. These devices stimulate the imagination to conceive a variety of other new electromechanical devices. Therefore, it is predicted that the marriage of the ultrasonics and integrated electronics technologies will give birth to an exciting and fruitful new field of investigation.