Electrostatically Variable Surface Acoustic Wave Delay Lines

A novel design for generating variable time delays in surface acoustic wave devices is presented. This design, referred to as the Modified In-Plane Field Design, uses an electric field applied to the propagation path of the SAW to modulate the time delay. The electric field is generated in the plane of the substrate by applying a DC voltage to an interdigital transducer (IDT) which is transverse to the input and output IDTs. An advantage of this device, compared to conventional in-plane field devices, is that its sensitivity can be increased without affecting the aperture of the SAW transducers. To test this geometry, devices which operated at 100 MHz were fabricated on 128° Y cut, X propagating Lithium Niobate (LiNb03). Various transverse IDTs were used to determine the effects of electrode spacing on sensitivity. The results of this test show that the device has two operating regions, nonlinear for low voltages and linear for higher voltages. The performance of this device was compared to two existing designs that were also fabricated and tested. These tests indicate that the Modified In-Plane Field Design can be configured for higher sensitivities