William J. Tanski

Heterojunction acoustic charge transport devices on GaAs

We have demonstrated a new type of buried‐channel acoustic charge transport device in which charge is transported in an (Al,Ga)As/GaAs/(Al,Ga)As heterojunction channel. Traveling‐wave potential wells, associated with a surface acoustic wave (SAW) propagating on the 〈100〉 surface of a GaAs crystal, transport electrons at the SAW velocity by means of a large‐signal acoustoelectric interaction. Heterojunction acoustic charge transport (HACT) delay lines have been fabricated, and the transport of charge demonstrated. Charge packets with up to 16×106 electrons/cm were measured in a delay 1.4 μs long. The HACT device is much simpler, the transport channel is more reliably produced (by molecular beam epitaxy or metalorganic chemical vapor deposition), and the device has potential for higher dynamic range when compared to the previously developed acoustic charge transport technology. This new device type is useful for the implementation of high‐speed monolithic signal processors.

Surface acoustic wave frequency trimming of resonant and traveling‐wave devices on quartz

A procedure for the postfabrication frequency adjustment (trimming) of narrow‐band surface acoustic wave devices on quartz is described. This procedure utilizes selective etching of a quartz substrate by means of a tetrafluoromethane + oxygen (CF4+O2) plasma, to permanently change the physical configuration of the transducers by increasing the step height of metal electrode structures. An increase in energy storage at the step edges and an increase in transducer reflectivity (for resonators) contribute to a reduction in device frequency. This technique is simple, it may be readily implemented using several types of equipment, and the long‐term aging rate of a devce is not changed. The technique may be used for resonators, which may be trimmed by etching the transducers only, and with delay‐line type filters having any electrode configuration.

Detection of Surface-Wave Three-Phonon Interaction

The resultant surface phonon generated by the interaction of two noncollinear surface phonons has been detected on the (111) face of a single-crystal copper sample. Detection was accomplished by optical probing of the two primary surface waves and the resultant phonons generated in the interaction.

Heterojunction acoustic charge transport device technology

A brief description of the general acoustic charge transport (ACT) device and the operation of ACT devices is given. The application of GaAs-AlGaAs heterojunctions to ACT technology and the design of heterojunction ACT (HACT) devices is discussed. The performance characteristics of experimental HACT devices are presented. It is shown that Nyquist rate bandwidths with rolloffs less than 3dB can be obtained at signal output taps, and that transport currents of 100 mu A can be carried by the SAW with less than 4 mW/ lambda acoustic drive power. In addition, heterojunction FETs (field-effect transistors) with gain up to 10 GHz have been fabricated on HACT substrates, illustrating the compatibility of integrated circuitry with the HACT device substrate.<<ETX>>

A configuration and circuit analysis for one‐port SAW resonators

One‐port SAW resonators fabricated on ST‐quartz with recessed electrode transducers and grooved reflector have been found to yield excellent device response characteristics. This configuration is superior to all others tested and is usable over a wide frequency range. The device structure and experimental data are presented. Also, an accurate and easy‐to‐use calculation scheme is presented to derive the resonance equivalent circuit parameters from experimental data.

A 3.35 microsecond HACT transversal filter

A heterojunction acoustic charge transport (HACT) transversal filter with a 3.35- mu s integration time is reported. This is the longest acoustic charge transport device reported to date. The device operates at an acoustic clock frequency of 144 MHz and at an acoustic power of 100 mW. The output signal is generated by 480 equally weighted taps. The multiple output tap structure results in the device exhibiting 12 dB of gain when embedded in a 50- Omega system. Measurements of the 1-dB compression point, the third-order intercept, and the noise floor show the dynamic range of the device to be in excess of 80 dB over the 300-kHz bandwidth of the filter.<<ETX>>

Further investigation of noncollinear surface‐wave interactions

Two noncollinear surface waves of 5 and 7 MHz have been excited on the surface of single‐crystal copper samples in such directions that the waves could interact via the nonlinearities of the medium to produce a third surface wave at the sum frequency of 12 MHz. Using optical techniques, the three waves involved have been detected on two crystal surfaces, the (001) and (111) planes of copper, and the amplitude of each of the waves has been measured.

A base-band NDS electrode configuration for HACT devices

Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal.<<ETX>>