• B R SINGH

      Articles written in Bulletin of Materials Science

    • GaAs MESFET and related processes

      O P Daga J K Singh B R Singh H S Kothari W S Khokle

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      Since inception of GaAs MESFET in 1971, growth and processing technology of GaAs has matured to the extent that the analogue as well as digital IC production is persued at the industrial level. The ever increasing demand for higher frequency of operation, low noise figure and higher gain has led to newer device structures such as HEMT and HJBT based on GaAs and related compounds. Furthermore there exists exciting and proven capabilities in GaAs and related compounds to generate, detect and convert light into electrical signals. This has opened up vast field of opto-electronic devices and their integration with MESFET and other conventional devices.

      Basic building block of all these developmental activities still remains the GaAs MESFET, which have also been extensively used as low noise amplifiers, mixers, oscillators and high power amplifiers in descrete form. This paper reviews the design aspects, fabrication technology, d.c. and microwave characterization for both low noise and high power MESFET.

      Various technological advancements like via-hole for source grounding, air-bridge technology for low parasitic interconnects and polymide passivation, which have helped in further improvement in terms of higher frequency of operation, low noise and high power output are reviewed.

      Finally some representative results on the devices fabricated at CEERI are also presented.

    • On the measurement of microwave absorption of bulk YBaCuO superconductors in X-band (8–12 GHz)

      J K Singh H S Kothari O P Daga B R Singh W S Khokle

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      Microwave absorption at the surface of highTc YBaCUO superconducting sample has been determined in X-band by measuring VSWR. Power reflectivity >98% has been observed in the frequency range of 8·2–10·5 GHz indicating very low absorption at the surface. At some of the frequencies, however, negligible microwave loss has been observed.

    • On the structural and electrical properties of metal–ferroelectric–high k dielectric–silicon structure for non-volatile memory applications

      PRASHANT SINGH RAJESH KUMAR JHA RAJAT KUMAR SINGH B R SINGH

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      In this article, we report the structural and electrical properties of metal–ferroelectric–high k dielectric–silicon (MFeIS) gate stack for non-volatile memory applications. Thin film of sputtered SrBi$_2$Nb$_2$O$_9$ (SBN) was used as ferroelectric material on 5–15 nm thick high-k dielectric (Al$_2$O$_3$) buffer layer deposited using plasma-enhanced atomic layer deposition (PEALD). The effect of annealing on structural and electrical properties of SBN and Al$_2$O$_3$ films was investigated in the temperature range of 350–1000$^{\circ}$C. X-ray diffraction results of the SBN and Al$_2$O$_3$ show multiple phase changes with an increase in the annealing temperature. Multiple angle ellipsometry data show the change in the refractive index ($n$) of SBNfilm from 2.0941 to 2.1804 for non-annealed to samples annealed at 600$^{\circ}C. For Al$_2$O$_3$ film, $n$ < 1.7 in the case of PEALDand $n$ > 1.7 for sputtered film was observed. The leakage current density in MFeIS structure was observed to two orders of magnitude lower than metal/ferroelectric/silicon (MFeS) structures. Capacitance–voltage (C–V) characteristics for the voltage sweep of $−$10 to 10 V in dual mode show the maximum memory window of 1.977 V in MFeS structure, 2.88 Vwith sputtered Al$_2$O$_3$ and 2.957 V with PEALD Al$_2$O$_3$ in the MFeIS structures at the annealing temperature of 500$^{\circ}$C.

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