Emilio J. Branciforte

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.

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 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>>

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>>

Interaction Mechanisms Between Acoustic Waves and MESFETS on GaAs

This paper describes the linear and nonlinear interactions between surface acoustic waves and MESFETs on GaAs. The output signals generated by SAW/MESFETs are compared to the outputs of an identical MESFET operated in a common source amplifier circuit. A model of the linear SAW/MESFET is presented which is based upon the conventional MESFET model and includes an additional voltage source to account for the transducer response of the structure. The nonlinear signals generated by the MESFET and the SAW/MESFET are shown to be the derivatives of the linear signals. In addition, the linear and nonlinear output signals generated by a SAW/diode were characterized as functions of bias. The linear signal is related to the transducer response of the structure and to its impedance as a function of bias. Nonlinear output peaks are present at bias voltages corresponding to the onset of forward conduction and the complete penetration of the depletion region through the conducting layer.