Critical fabrication processes for programmable HACT DPTFs

The type of acoustic charge transport (ACT) device which has generated the most widespread interest among electronics system designers is the digitally programmable transversal filter (DPTF). A heterojunction ACT (HACT) DPTF, having 128 taps with 5-b tap resolution and on-chip buffer amplifiers for input and output, is described. The device is being fabricated by a combination of epitaxial and ion-implantation processes, and it employs three metal layers. In addition to providing very high resolution for fine-line lithography and large depth of field for the nonplanar circuits in a HACT DPTF, E-beam lithography allows easy adjustment of critical circuit elements to adjust for parasitics, without the need to generate new mask layers. A discussion of the expected performance of this device is presented