The purpose of this paper is to prove a maximal ergodic theorem for Abel means of a strongly meas... more The purpose of this paper is to prove a maximal ergodic theorem for Abel means of a strongly measurable semi-group Γ={T t ;t^0} of linear contractions on a complex Li-space satisfying | T t f | ^ c a.e. for any t Ξ> 0 and any integrable / with I /1 ^ c a.e. Applying the obtained maximal ergodic theorem, individual and dominated ergodic theorems for Abel means are also proved. These results extend results obtained by D. A. Edwards for sub-Markovian semi-groups. 2* The maximal ergodic theorem. Let (X, ^ μ) be a σ-ίinite
Coplanar waveguides are fabricated by directly bonding 17-μm Al foils to Si substrates with diffe... more Coplanar waveguides are fabricated by directly bonding 17-μm Al foils to Si substrates with different resistivities. A lower insertion loss is observed for a Si substrate with higher resistivity since the substrate loss is decreased. Calculation using an analytical model shows that the insertion loss increases by reducing the thickness of conductors, which demonstrates the superiority of direct bonding of metal foils for realizing low-loss passive components to be integrated on semiconductor substrates.
Magnetotransport behavior of two-dimensional X-band electrons created in modulation-doped very e ... more Magnetotransport behavior of two-dimensional X-band electrons created in modulation-doped very e thin (25-75 A) AlAs quantum wells was studied. Effective-mass analysis based on temperature-0 dependent magnetoresistances clearly showed X,-X,~crossover at an AlAs thickness of about 45 A. This value is much smaller than that in an A1As/GaAs type-II superlattice (60 A). Origins of this difference were discussed in terms of the effect of doping and degeneracy change and of the change of strain due to the structure difference. Despite the importance of A1As in potential optical and electronical applications, fundamental properties of this material have not yet been sufficiently clarified. Optical measurements such as photoluminescence and optical detected magnetic resonance, etc. , however, have led to extensive reports about the I-X transition' and the X-band crossover in A1As/GaAs type-II superlattices (SL's). As a result, in undoped short-period A1As/GaAs
The subband structure of two-dimensional X-band electrons in modulation-doped very thin (25-75 Å)... more The subband structure of two-dimensional X-band electrons in modulation-doped very thin (25-75 Å) AlAs quantum wells was studied in magnetotransport experiments and analyzed in self-consistent calculations. Effective mass estimation based on temperature dependent magnetoresistances clearly showed Xz-Xxy crossover at an AlAs thickness of about 45 Å, which is much less than the crossover thickness in AlAs/GaAs type II superlattices (60 Å). Considering the results of self-consistent calculations together with some observed anomalies in Xxy electron magnetoresistances, we can conclude that this difference is due to the effect of doping and to the degeneracy change in k-space occurring at the crossover thickness of AlAs.
Telephone +87 462 40 2612 Fascimile +81 462 40 2872 New functional devices based on resonant tunn... more Telephone +87 462 40 2612 Fascimile +81 462 40 2872 New functional devices based on resonant tunneling (RT) phenomena [1J have attracted much attention owing to the novel negative differential resistance (NDR) characteristics of these devices. A recently proposed logic gate, called MOBILE [2] (monostable-bistable transition logic element), takes advantage of the NDR feature of RT devices and has demonstrated its promising usefulness in constmcting complicated computing systems such as cellular automata and neural networks [3,4J. In this letter, we propose and demonstrate a new approach in building devices suitable for MOBILE circuits. Our approach is based on integrating resonant tunneling diode (RTD) and FET in parallel' A MOBILE consists of two resonant tunneling transistors (RTTs) connected in series and is driven by an oscillatingbias voltage (\*.) to produce themonostablc-to-bistable transition (Fig. 1). The transition takes place when V0,". passes through twice the peak voltage (2Vp), where one stable point splits into two
Resonant-tunneling diodes (RTDs) exhibit faster switching times (1.5~~) than any other semiconduc... more Resonant-tunneling diodes (RTDs) exhibit faster switching times (1.5~~) than any other semiconductor devices [l]. Their negative differential resistance characteristics provide opportunities to implement functions, such as multiple-valued logic, with reduced circuit complexity. Experimental results for a lOGHz resonant-tunneling 3-valued quantizer and a 4b flash A/D converter employing such quantizers are presented. The number of active devices is reduced to 240, Yi the number required in conventional A/D converters. Maximum sampling frequencies of lOGHz are predicted.
Monolithic integration technology for resonant tunneling diodes (RTDs), Schottky barrier diodes (... more Monolithic integration technology for resonant tunneling diodes (RTDs), Schottky barrier diodes (SBDs), and 0.1-µm-gate high electron mobility transistors (HEMTs) was developed. The integration process was investigated to overcome the difficulty in fabricating both RTDs with a mesa height of 530 nm and HEMTs with a gate length of 0.1 µm. The HEMT and SBD structures were grown by metalorganic chemical vapor deposition (MOCVD) on a 2-inch InP substrate. The RTD structure was regrown by molecular beam epitaxy (MBE) on the top layer grown by MOCVD. The characteristics of the fabricated devices showed good uniformity. An analog-to-digital converter and a selector circuit fabricated with these devices operated properly. The presented integration technology is a promising way to provide novel circuits with RTDs, SBDs and 0.1-µm-gate HEMTs.
Coplanar waveguides (CPWs) are fabricated by directly bonding 17 μm Al foils to Si substrates wit... more Coplanar waveguides (CPWs) are fabricated by directly bonding 17 μm Al foils to Si substrates with different resistivities and wet etching. Their RF characteristics are compared with those of CPWs fabricated on 0.8 μm thick evaporated Al layers. A lower insertion loss is observed for Si substrates with higher resistivity irrespective of the thickness of conductors because the substrate loss is decreased. For a 10000-Ω · cm Si substrate, Al-foil-based CPWs reveal a ∼0.7 dB cm−1 lower insertion loss in comparison with evaporated-Al-based CPWs at 1 GHz. These features agree with the calculation, which implies the superiority of direct bonding of metal foils for realizing low-loss passive components.
Herein, the authors experimentally characterise the dynamics of voltage edges oscillating in a tr... more Herein, the authors experimentally characterise the dynamics of voltage edges oscillating in a transmission line with regularly spaced two series-connected tunnel diodes (TDs). They clearly observe the mutually synchronised behaviour of the edges supported by each TD, which can be utilised to generate large-amplitude and low-phase-noise oscillatory voltages. They establish the fact that the response time of the device for state-transition is the key to qualitatively determine the edge oscillation, i.e. a single large-amplitude edge develops for sufficiently a large response time, whereas two larger and smaller edges coexist and are synchronised for short response time.
ABSTRACT This paper discusses ohmic contact formation of Sn-based alloys on n-InSb. Most critical... more ABSTRACT This paper discusses ohmic contact formation of Sn-based alloys on n-InSb. Most critical problem, we encountered when using a Sn/Au/Ni/Ti/Au metal stack, is an anomalous alloy extension of the ohmic metal. This was found to be resulted from rapid diffusion of Au. It is demonstrated that by removing the Au under the Ti barrier layer good contact resistance of less than 0.1 Ωmm can be obtained without anomalous alloy extension.
The purpose of this paper is to prove a maximal ergodic theorem for Abel means of a strongly meas... more The purpose of this paper is to prove a maximal ergodic theorem for Abel means of a strongly measurable semi-group Γ={T t ;t^0} of linear contractions on a complex Li-space satisfying | T t f | ^ c a.e. for any t Ξ> 0 and any integrable / with I /1 ^ c a.e. Applying the obtained maximal ergodic theorem, individual and dominated ergodic theorems for Abel means are also proved. These results extend results obtained by D. A. Edwards for sub-Markovian semi-groups. 2* The maximal ergodic theorem. Let (X, ^ μ) be a σ-ίinite
Coplanar waveguides are fabricated by directly bonding 17-μm Al foils to Si substrates with diffe... more Coplanar waveguides are fabricated by directly bonding 17-μm Al foils to Si substrates with different resistivities. A lower insertion loss is observed for a Si substrate with higher resistivity since the substrate loss is decreased. Calculation using an analytical model shows that the insertion loss increases by reducing the thickness of conductors, which demonstrates the superiority of direct bonding of metal foils for realizing low-loss passive components to be integrated on semiconductor substrates.
Magnetotransport behavior of two-dimensional X-band electrons created in modulation-doped very e ... more Magnetotransport behavior of two-dimensional X-band electrons created in modulation-doped very e thin (25-75 A) AlAs quantum wells was studied. Effective-mass analysis based on temperature-0 dependent magnetoresistances clearly showed X,-X,~crossover at an AlAs thickness of about 45 A. This value is much smaller than that in an A1As/GaAs type-II superlattice (60 A). Origins of this difference were discussed in terms of the effect of doping and degeneracy change and of the change of strain due to the structure difference. Despite the importance of A1As in potential optical and electronical applications, fundamental properties of this material have not yet been sufficiently clarified. Optical measurements such as photoluminescence and optical detected magnetic resonance, etc. , however, have led to extensive reports about the I-X transition' and the X-band crossover in A1As/GaAs type-II superlattices (SL's). As a result, in undoped short-period A1As/GaAs
The subband structure of two-dimensional X-band electrons in modulation-doped very thin (25-75 Å)... more The subband structure of two-dimensional X-band electrons in modulation-doped very thin (25-75 Å) AlAs quantum wells was studied in magnetotransport experiments and analyzed in self-consistent calculations. Effective mass estimation based on temperature dependent magnetoresistances clearly showed Xz-Xxy crossover at an AlAs thickness of about 45 Å, which is much less than the crossover thickness in AlAs/GaAs type II superlattices (60 Å). Considering the results of self-consistent calculations together with some observed anomalies in Xxy electron magnetoresistances, we can conclude that this difference is due to the effect of doping and to the degeneracy change in k-space occurring at the crossover thickness of AlAs.
Telephone +87 462 40 2612 Fascimile +81 462 40 2872 New functional devices based on resonant tunn... more Telephone +87 462 40 2612 Fascimile +81 462 40 2872 New functional devices based on resonant tunneling (RT) phenomena [1J have attracted much attention owing to the novel negative differential resistance (NDR) characteristics of these devices. A recently proposed logic gate, called MOBILE [2] (monostable-bistable transition logic element), takes advantage of the NDR feature of RT devices and has demonstrated its promising usefulness in constmcting complicated computing systems such as cellular automata and neural networks [3,4J. In this letter, we propose and demonstrate a new approach in building devices suitable for MOBILE circuits. Our approach is based on integrating resonant tunneling diode (RTD) and FET in parallel' A MOBILE consists of two resonant tunneling transistors (RTTs) connected in series and is driven by an oscillatingbias voltage (\*.) to produce themonostablc-to-bistable transition (Fig. 1). The transition takes place when V0,". passes through twice the peak voltage (2Vp), where one stable point splits into two
Resonant-tunneling diodes (RTDs) exhibit faster switching times (1.5~~) than any other semiconduc... more Resonant-tunneling diodes (RTDs) exhibit faster switching times (1.5~~) than any other semiconductor devices [l]. Their negative differential resistance characteristics provide opportunities to implement functions, such as multiple-valued logic, with reduced circuit complexity. Experimental results for a lOGHz resonant-tunneling 3-valued quantizer and a 4b flash A/D converter employing such quantizers are presented. The number of active devices is reduced to 240, Yi the number required in conventional A/D converters. Maximum sampling frequencies of lOGHz are predicted.
Monolithic integration technology for resonant tunneling diodes (RTDs), Schottky barrier diodes (... more Monolithic integration technology for resonant tunneling diodes (RTDs), Schottky barrier diodes (SBDs), and 0.1-µm-gate high electron mobility transistors (HEMTs) was developed. The integration process was investigated to overcome the difficulty in fabricating both RTDs with a mesa height of 530 nm and HEMTs with a gate length of 0.1 µm. The HEMT and SBD structures were grown by metalorganic chemical vapor deposition (MOCVD) on a 2-inch InP substrate. The RTD structure was regrown by molecular beam epitaxy (MBE) on the top layer grown by MOCVD. The characteristics of the fabricated devices showed good uniformity. An analog-to-digital converter and a selector circuit fabricated with these devices operated properly. The presented integration technology is a promising way to provide novel circuits with RTDs, SBDs and 0.1-µm-gate HEMTs.
Coplanar waveguides (CPWs) are fabricated by directly bonding 17 μm Al foils to Si substrates wit... more Coplanar waveguides (CPWs) are fabricated by directly bonding 17 μm Al foils to Si substrates with different resistivities and wet etching. Their RF characteristics are compared with those of CPWs fabricated on 0.8 μm thick evaporated Al layers. A lower insertion loss is observed for Si substrates with higher resistivity irrespective of the thickness of conductors because the substrate loss is decreased. For a 10000-Ω · cm Si substrate, Al-foil-based CPWs reveal a ∼0.7 dB cm−1 lower insertion loss in comparison with evaporated-Al-based CPWs at 1 GHz. These features agree with the calculation, which implies the superiority of direct bonding of metal foils for realizing low-loss passive components.
Herein, the authors experimentally characterise the dynamics of voltage edges oscillating in a tr... more Herein, the authors experimentally characterise the dynamics of voltage edges oscillating in a transmission line with regularly spaced two series-connected tunnel diodes (TDs). They clearly observe the mutually synchronised behaviour of the edges supported by each TD, which can be utilised to generate large-amplitude and low-phase-noise oscillatory voltages. They establish the fact that the response time of the device for state-transition is the key to qualitatively determine the edge oscillation, i.e. a single large-amplitude edge develops for sufficiently a large response time, whereas two larger and smaller edges coexist and are synchronised for short response time.
ABSTRACT This paper discusses ohmic contact formation of Sn-based alloys on n-InSb. Most critical... more ABSTRACT This paper discusses ohmic contact formation of Sn-based alloys on n-InSb. Most critical problem, we encountered when using a Sn/Au/Ni/Ti/Au metal stack, is an anomalous alloy extension of the ohmic metal. This was found to be resulted from rapid diffusion of Au. It is demonstrated that by removing the Au under the Ti barrier layer good contact resistance of less than 0.1 Ωmm can be obtained without anomalous alloy extension.
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Papers by Koichi Maezawa