Robert Frederick Fischer

Electrical activity of defects in molecular beam epitaxially grown GaAs on Si and its reduction by rapid thermal annealing

The electrical activity of defects in GaAs grown on Si by molecular beam epitaxy (MBE) has been examined by studying the diode characteristics and deep level transient spectroscopy (DLTS) of Schottky barriers. The defects are not apparent from the forward bias diode characteristics but they are indicated by large leakage current and early breakdown under reverse‐biased conditions. Post‐growth rapid thermal annealing (RTA) has been found to significantly improve the diode behavior making it almost comparable to GaAs‐on‐GaAs. The reverse current in the as‐grown material shows a very weak temperature dependence, indicating that its origin is not thermionic emission or carrier generation. It is speculated that a large part of this current is due to defect‐assisted tunneling, which is reduced by RTA. DLTS indicated only a modest increase in the concentrations of the well‐known electron traps typical of MBE GaAs with no evidence for new levels in the upper half of the band gap.

Functional speed measurements of propagating devices utilizing cylindrical domains in orthoferrites and garnets

Functional speed, measurements have been made on field-access T-bar and Y-bar bubble devices utilizing flux-grown crystal platelets of Gd 2.34 Tb 0.66 Fe 5 O 12 , Eu 2 Er 1 Ga 0.65 Fe 4.35 O 12 , Sm 0.55 Tb 0.45 FeO 3 , and epitaxially grown films of Eu 1 Er 2 Ga 0.7 Fe 4.3 O 12 . Propagation rates of 250 kbit/s with bias margins of ±7 percent have been achieved with epitaxial garnet films. A propagating device utilizing an epitaxial garnet film has demonstrated a storage capability of 1.6 Mbit/in2.The device, Which includes a propagation turn, has been worse case tested. This resulted in a bias margin of ±7 percent with a 25-Oe 100-kHz rotating in-plane field.

Reversible, Diodeless, Twistor Shift Register

A twistor shift register has been built and operated successfully. The design utilizes interaction effects which exist between magnetized regions on a magnetic wire. Only a single magnetic wire is required for a complete register. The information is stored as magnetically polarized zones which can be moved along the wire by means of a five phase pulse source.No diodes are required. Therefore, drive powers can be greatly decreased since the only threshold consideration is the magnetic material itself. Bi‐directional operation is easily secured. The upper frequency limit has not been established; however, a several hundred kilocycle bit rate should be possible. Physically, the register could be made of no more than magnetic and copper wire. This should make fabrication considerably cheaper than conventional shift registers.

MICROSTRUCTURE ARRAYS PRODUCED BY ION MILLING

Techniques have been developed using argon ion milling to produce high‐density microstructure arrays of permalloy magnetic dipoles for use in magnetic bubble devices. Ion milling is used to replace the chemical etch process in the usual photolithographic method, which results in an order‐of‐magnitude improvement in density. A 1000‐bit I and bar shift register has been made in which the spacing between elements in 7.5μ, and the width of the elements are ∼ 1μ. The entire structure is 0.25 mm (or 10 mil) square.

Parallel-to-serial converter utilizing property of domain wall motion in permalloy wires

The domain wall motion phenomenon in some Permalloy wires, as reviewed in a companion paper, offers the possibility of magnetically realizing useful functional packages. Several low-current devices of lengths below 300 bits were developed which exploit this phenomenon. This paper describes a parallel-to-serial converter and discusses the technology associated with fabricating this and other low-current functional devices. The converter is capable of accepting 64 bits of parallel data in 10 μs and delivering it sequentially upon command at the rate of up to 50 kbits/s.