John N. Randall

Characteristics of micromachined switches at microwave frequencies

This article reviews the fundamental characteristics of micromechanical membrane switches operating at microwave frequencies. The construction and theory of operation of capacitive membrane switches is reviewed. Measurement and modeling of the electromechanical and microwave properties of these switches are presented. The inherent advantages of these switches relative to semiconductor switches is discussed.

Realization of a three‐terminal resonant tunneling device: The bipolar quantum resonant tunneling transistor

A new three‐terminal resonant tunneling structure in which current transport is controlled by directly modulating the potential of the quantum well is proposed and demonstrated. Typical current gains of 50 at room temperature are observed.

Pseudomorphic bipolar quantum resonant-tunneling transistor

A bipolar tunneling transistor in which ohmic contact is made to the strained p/sup +/ InGaAs quantum well of a double-barrier resonant-tunneling structure is discussed. The heterojunction transistor consists of an n-GaAs emitter and collector, undoped AlGaAs tunnel barriers, and a pseudomorphic p/sup +/ InGaAs quantum-well base. By making ohmic contact to the p-type quantum well, the hole density in the quantum-well base is used to modulate the base potential relative to the emitter and collector terminals. With control of the quantum-well potential, the tunneling current can be modulated by application of a base-to-emitter potential. The authors detail the physical and electrical characteristics of the device. It is found that the base-emitter voltages required to bias the transistor into resonance are well predicted by a self-consistent calculation of the electrostatic potential. >

Nanoelectronics: Fanciful Physics or Real Devices

Remarkable advances in microfabrication technology have allowed physicists to probe into the size regime where quantum mechanical effects begin to dominate transport. When 1D conducting wires made from two‐dimensional electron gases (2DEGs) approach the same size as the deBroglie wavelength of electrons, electronic transport is determined by transmission through a small number of ‘‘waveguide modes’’ of the 1D channel. Low temperature experiments in this size regime show significant wavefunction interference effects. A number of devices based upon these physical phenomena have been proposed. Quantum localization has also been explored in perpendicular electronic transport through heteroepitaxial structures, the simplest case being one‐dimensional resonant tunneling structures that exhibit strong quantum interference up to room temperature. Three‐terminal devices that directly modulate this interference have been demonstrated. Ultimate scaling limitations of heterojunction tunneling devices will only be con...

Co-integrated resonant tunneling and heterojunction bipolar transistor full adder

We present the first resonant tunneling bipolar transistor integrated circuits operating at room temperature. The circuits are comprised of co-integrated resonant tunneling and double heterojunction bipolar transistors based on III-V heteroepitaxy on InP substrates. The resonant tunneling bipolar transistors exhibit a peak-to-valley collector current ratio exceeding 70 which is higher than previous room temperature reports. Using this technology we demonstrate a 3-transistor XNOR, a 6-transistor XOR, a 5-transistor CARRY, and a 17-transistor full adder, all using a 3 V supply.<<ETX>>

Room Temperature Hot Electron Transistors with InAs-Notched Resonant-Tunneling-Diode Injector

Room temperature operation is achieved in In(GaAl)As/InGaAs resonant-tunneling hot electron transistors (RHET) grown by molecular beam epitaxy on InP substrates. RHETs with base widths of 10, 40 and 60 nm are fabricated and all exhibit room temperature dc current gain greater than 2, with gain as high as 12 observed at resonance in the 40 nm base device. To our knowledge these are the first In(GaAl)As hot electron transistors to exhibit 300 K gain of this magnitude. In addition, the transistors also exhibit strong negative transconductance and a unique negative peak-to-valley current ratio. S-parameter measurements of the 40(60) nm base RHET give values for fT and fMAX of 67(54) and 41(11) GHz respectively.

Co-integration of resonant tunneling and double heterojunction bipolar transistors on InP

The authors report the first co-integration of resonant tunneling and heterojunction bipolar transistors. Both transistors are produced from a single epitaxial growth by metalorganic molecular beam epitaxy, on InP substrates. The fabrication process yields 9- mu m/sup 2/-emitter resonant tunneling bipolar transistors (RTBTs) operating at room temperature with peak-to-valley current ratios (PVRs) in the common-emitter transistor configuration, exceeding 70, at a resonant peak current density of 10 kA/cm/sup 2/, and a differential current gain at resonance of 19. The breakdown voltage of the In/sub 0.53/Ga/sub 0.47/As-InP base/collector junction, V/sub CBO/, is 4.2 V, which is sufficient for logic function demonstrations. Co-integrated 9- mu m/sup 2/-emitter double heterojunction bipolar transistors (DHBTs) with low collector/emitter offset voltage, 200 mV, and DC current gain as high as 32 are also obtained. On-wafer S-parameter measurements of the current gain cutoff frequency (f/sub T/) and the maximum frequency of oscillation (f/sub max/) yielded f/sub T/ and f/sub max/ values of 11 and 21 GHz for the RTBT and 59 and 43 GHz for the HBT, respectively.<<ETX>>

Atomic precision lithography on Si

Lithographic precision is as or more important than resolution. For decades, the semiconductor industry has been able to work with ±5% precision. However, for other applications such as micronanoelectromechanical systems, optical elements, and biointerface applications, higher precision is desirable. Lyding et al. [Appl. Phys. Lett. 64, 11 (1999)] have demonstrated that a scanning tunneling microscope can be used to remove hydrogen (H) atoms from a silicon (100) 2 × 1 H-passivated surface through an electron stimulated desorption process. This can be considered e-beam lithography with a thin, self-developing resist. Patterned hydrogen layers do not make a robust etch mask, but the depassivated areas are highly reactive since they are unsatisfied covalent bonds and have been used for selective deposition of metals, oxides, semiconductors, and dopants. The depassivation lithography has shown the ability to remove single H atoms, suggesting the possibility of precise atomic patterning. This patterning proces...

Fabrication of micromechanical switches for routing radio frequency signals

Micromechanical switches have several advantages over other switch technologies for the routing of microwave and mm‐wave signals. They offer low loss, low switching power, very low standby power, and are extremely linear. The switching speeds are very slow compared to solid state switches; however, for a number of applications, their specifications appear attractive. For instance, electronically steerable antenna arrays operating at 10, 20, and 30 GHz need phase shifters for each antenna element. Micromechanical RF switches that offered lower losses could find significant applications as phase shifters for telecommunications applications. We describe the fabrication of membrane micromechanical RF switches that switch signals of 10 GHz and higher. Dry etching plays a critical role in fabrication. In particular the isotropic removal of a sacrificial polymer layer between the bottom electrode and the membrane is a critical process. Reasonable rates must be obtained at moderate temperatures and there must be ...

Microstructure fabrication and transport through quantum dots

We report the microfabrication techniques used to produce devices which study electronic transport through quantum dots. Molecular‐beam epitaxy, electron‐beam lithography, and reactive ion etching have been utilized in this effort. The minimum physical lateral size of the dots reported here is 0.1×0.2 μm. Transport shows some degradation in I–V characteristics with respect to much larger resonant tunneling diodes. Current densities observed suggest the electrical size of diodes is smaller than the physical size. A surface depletion region of 500 A may account for this effect. Telegraph noise is observed as a result of single electron trapping in the structure. No clear evidence of lateral quantization has been observed.