A molecule containing a nitroamine redox center (2'-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol) was used in the active self-assembled monolayer in an electronic device. Current-voltage measurements of the device exhibited negative differential resistance and an on-off peak-to-valley ratio in excess of 1000:1.

https://science.sciencemag.org/content/sci/286/5444/1550.full.pdf

Large On-Off Ratios and Negative Differential Resistance in a Molecular Electronic Device.

Many semiconductor quantum devices utilize a novel tunneling transport mechanism that allows picosecond device switching speeds The negative differential resistance characteristic of these devices, achieved due to resonant tunneling, is also ideally suited for the design of highly compact, self-latching logic circuits As a result, quantum device technology is a promising emerging alternative for high-performance very-large-scale-integration design The bistable nature of the basic logic gates implemented using resonant tunneling devices has been utilized in the development of a gate-level pipelining technique, called nanopipelining, that significantly improves the throughput and speed of pipelined systems The advent of multiple-peak resonant tunneling diodes provides a viable means for efficient design of multiple-valued circuits with decreased interconnect complexity and reduced device count as compared to multiple-valued circuits in conventional technologies This paper details various circuit design accomplishments in the area of binary and multiple-valued logic using resonant tunneling diodes (RTD's) in conjunction with high-performance III-V devices such as heterojunction bipolar transistors (HBT's) and modulation doped field-effect transistors (MODFET's) New bistable logic families using RTD+HBT and RTD+MODFET gates are described that provide a single-gate, self-latching majority function in addition to basic NAND, NOR, and inverter gates

/pdf/digital-circuit-applications-of-resonant-tunneling-devices-393fsr9ny8.pdf

Digital circuit applications of resonant tunneling devices

A 50-nW standby power compound semiconductor tunneling-based static random access memory SRAM (TSRAM) cell is demonstrated by combining ultralow current-density resonant-tunneling diodes (RTDs) and heterostructure field-effect transistors (HFETs) in one integrated process on an InP substrate. This power represents over two orders of magnitude improvement over previous III-V static memory cells. By increasing the number of vertically integrated RTD's we obtain a 100 nW tri-state memory cell. The cell concept applies to any material system in which low current-density negative differential resistance devices are available.

RTD/HFET low standby power SRAM gain cell

The rapid development of heterojunction bipolar transistor (HBT) technologies has led to the demonstration of high power single-chip microwave amplifiers. Because HBTs are operated at high power densities, the ultimate limits on the performance of HBTs are imposed by thermal considerations. The authors address a thermal phenomenon observed when a multifinger power HBT is operating at high power densities. This phenomenon, referred to as the collapse (of current gain), occurs when suddenly one finger of the HBT draws most of the collector current, leading to an abrupt decrease of current gain. A quantitative model and the condition separating the normal operation region and the collapse are presented. Critical difference of the collapse in the constant l/sub b/ and constant V/sub be/ modes of operation is discussed for the common-emitter l-V characteristics. The collapse in the common-base l-V characteristics and its relationship with avalanche breakdown are also described. A solution to eliminate the collapse is experimentally verified. >

Current gain collapse in microwave multifinger heterojunction bipolar transistors operated at very high power densities

This paper describes a new high-density low-power circuit approach for implementing static random access memory (SRAM) using low current density resonant tunneling diodes (RTDs). After an overview of semiconductor random access memory architecture and technology, the concept of tunneling-based SRAM (TSRAM) is introduced. Experimental results for a compound semiconductor 1-bit 50-nW TSRAM gain cell using low current density (/spl sim/1 A/cm/sup 2/) RTDs and low-leakage heterostructure field effect transistors are presented. We describe a one-transistor TSRAM cell which could convert silicon dynamic RAM (DRAM) to ultradense SRAM if an ultralow current density (/spl sim/1 /spl mu/A/cm/sup 2/) silicon bistable device is developed. Finally, we present experimental and simulation results for a TSRAM cell using multipeaked I-V curve devices and a multivalued word line. This approach aims at increasing storage density through vertical integration of bistable devices such as RTD's.

Tunneling-based SRAM

The combination of resonant-tunneling diodes and heterostructure field-effect transistors provides a versatile technology for implementing microwave digital and mixed-signal applications. Here we demonstrate and characterize the first monolithic flash analog-to-digital converter (ADC) in this technology. The first-pass ADC achieved 2.7 effective bits at 2 gigasamples per second (Gsps) for a 220-MHz input signal. The one-bit quantizer achieved a single-tone spurious free dynamic range greater than 40 dB at 2 Gsps for a 220-MHz single-tone input with dithering.

A monolithic 4-bit 2-Gsps resonant tunneling analog-to-digital converter

GaInP/GaAs heterojunction bipolar transistors (HBTs) and both graded and abrupt AlGaAs/GaAs HBTs were fabricated. A total of 20 wafers were analyzed. Comparisons of the experimental results establish that the dominant carrier transport mechanism in GaInP/GaAs HBTs is the carrier diffusion through the base layer. This suggests that the conduction-band barrier across the GaInP/GaAs emitter-base junction is so small that the barrier spike does not affect the carrier transport. This result differs from other published results which, by studying device structures other than HBTs, determined the conduction band barrier to be as large as approximately 50% of the bandgap difference. The findings of the present investigation, however, agree well with another published work which also examined an HBT structure. The difference between these works is discussed. >

Current transport mechanism in GaInP/GaAs heterojunction bipolar transistors

Very-high-performance common-emitter InP/InGaAs single heterojunction bipolar transistors (HBTs) grown by metalorganic molecular beam epitaxy (MOMBE) are reported. They exhibit a maximum oscillation frequency (f/sub T/) of 180 GHz at a current density of 1*10/sup 5/ A/cm/sup 2/. this corresponds to an (R/sub B/C/sub BC/)/sub eff/=f/sub T//(8 pi f/sup 2//sub max/) delay time of 0.12 ps, which is the smallest value every reported for common-emitter InP/InGaAs HBTs. The devices have 11 mu m/sup 2/ total emitter area and exhibit current gain values up to 100 at zero base-collector bias voltage. The breakdown voltage of these devices is high with measured BV/sub CEO/ and BV/sub CEO/ of 8 and 17 V, respectively. >

High-speed InP/InGaAs heterojunction bipolar transistors

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. >

E.A. Beam

Papers

A monolithic 4-bit 2-Gsps resonant tunneling analog-to-digital converter

Current transport mechanism in GaInP/GaAs heterojunction bipolar transistors

High-speed InP/InGaAs heterojunction bipolar transistors

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

Monolithic 4 bit 2 GSps resonant tunneling analog-to-digital converter