Monostable-bistable Transition Logic Element Research Articles

Design of multi-threshold threshold gate using MOS-NDR circuits suitable for CMOS process

We demonstrate a multi-threshold threshold gate (MTTG) based on a series and parallel connection of several MOS-NDR circuits. A MOS-NDR circuit is made of five standard Si-based metal–oxide–semiconductor field-effect-transistor (MOS) devices. It can show the negative-differential-resistance (NDR) characteristic in its current–voltage (I–V) curve by adjusting suitable parameters for the MOS transistors. The operation principle of this MTTG is based on the monostable-bistable transition logic element (MOBILE), which the output voltage goes to the low or high state depending on the relative current-peak conditions of the series-connected NDR circuits by supplying a clocked voltage. The weight of this MTTG is defined by the gate width of the MOS device in the MOS-NDR circuit. It is different from the design using the area of the resonant tunneling diode as the weight in the other NDR-based MTTG circuit. A great advantage of this MOS-NDR-based MTTG is that we can design the application using the standard CMOS technology without the need of compound semiconductor.

An empirical I‐V model of tunneling real‐space transfer transistors for monostable–bistable transition logic element application

SummaryWe proposed an empirical I‐V model to represent the negative differential resistance (NDR) regime of fabricated tunneling real‐space transfer transistors (TRSTTs). For TRSTTs to have great potential in monostable–bistable transition logic element (MOBILE) design, our model is able to accurately reproduce the NDR regime including gate‐source‐bias‐controlled NDR values and modulated peak to valley drain current ratios. The modeled I‐V curves, tranconductances, and NDRs with multiple gate biases are in good agreement with measured data. The key parameters in the model have clear physical meanings, and the value of these parameters is easy to be extracted directly from the test I‐V curves. The model is used to simulate a practical MOBILE, and excellent agreement between the simulated and measured data was found. Copyright © 2015 John Wiley & Sons, Ltd.

Design of monostable–bistable transition logic element using the BiCMOS-based negative differential resistance circuit

The monostable---bistable transition logic element (MOBILE) is a promising application for negative differential resistance (NDR) circuit. Previously reported MOBILE is constructed by resonant tunneling diode (RTD) that is implemented by the molecular beam epitaxy (MBE) process. However in this paper, we first propose a NDR circuit composed of standard Si-based metal---oxide---semiconductor field-effect transistor (MOS) and SiGe-based heterojunction bipolar transistor (HBT). Then we demonstrate the inverter, NAND, and NOR gate operations using this MOS---HBT---NDR-based MOBILE circuit. The great advantage of this NDR-based application is that we can implement it using the standard SiGe BiCMOS process without the need for the MBE system.

Logic circuit design using monostable–bistable transition logic element based on standard BiCMOS process

We present a monostable–bistable transition logic element (MOBILE) based on the negative-differential-resistance (NDR) circuit. In particular, this circuit can be completely implemented using the standard BiCMOS process. A traditional MOBILE using two resonant tunneling diodes (RTD) connected in series is a functional logic circuit. The fabrication of RTD is utilized in the complicated molecular-beam-epitaxy (MBE) system. However, we present a MOBILE circuit that is completely made of standard Si-based metal-oxide-semiconductor field effect transistors and SiGe-based heterojunction bipolar transistors. By suitably determining the control voltages and input conditions, we can obtain the operation of the inverter, AND and OR logic gates. We also demonstrate the latch characteristic of this MOBILE circuit. This logic circuit is fabricated using the standard 0.35μm BiCMOS process without the need for the MBE system.

Monostable–Bistable Transition Logic Element Formed by Tunneling Real-Space Transfer Transistors With Negative Differential Resistance

We demonstrate three-terminal λ-type negative differential resistance (NDR) tunneling real-space transfer transistors (TRSTT) with InGaAs and a δ-doped GaAs dual-channel structure on a (100) GaAs substrate. The NDR mechanism is attributed to the electron tunneling transfer from a high-mobility InGaAs channel to a low-mobility δ-doped GaAs channel, as well as to a gate electrode through a Schottky cap layer. The maximum of the peak-to-valley current ratio and the transconductance of the peak current density (gm = ΔJP/ΔVGS) reach 3.3 and 72 mS/mm, respectively. The invert operation of MOBILE is realized by employing two TRSTTs connected in series at room temperature.

Complete Logic Functionality of Reconfigurable RTD Circuit Elements

Innovative nanoscale devices have been developed to enhance future circuit design to overcome physical barriers hindering the CMOS technology. Among the emerging nanodevices, resonant tunneling diodes (RTDs) have demonstrated promising electronic features due to their high-speed switching capability and functional versatility. Great circuit functionality can be achieved through integrating heterostructure FETs (HFETs) in conjunction with RTDs to modulate effective negative differential resistance. In this paper, we propose novel programmable logic elements (PLEs) implemented in threshold gates (TGs) and multithreshold TGs by exploring RTD/HFET monostable-bistable transition logic element (MOBILE) principles. Our three-input PLE can be configured through five binary control bits to realize all the three-variable logic functions, which is, to the best of our knowledge, the first single RTD-based structure that provides complete Boolean logic implementation. It is also a more efficient reconfigurable circuit element than a general lookup table that requires eight configuration bits for three-variable functions. We further extend the design concept to construct a more versatile four-input PLE. A comprehensive comparison of three- and four-input PLEs provides an insightful view of design tradeoffs between performance and area. We present the mathematical proof of PLE's logic completeness based on Shannon expansion, as well as the HSPICE simulation results of the programmable and primitive RTD/HFET gates that we have designed. An efficient control bit generating algorithm is developed by using a special encoding scheme to implement any given logic function. Based on our PLE structures, we propose a reconfigurable architecture, namely MORE, which offers dynamic reconfigurability without incurring latency overheads, due to the intrinsic self-latching property of MOBILE circuits. An efficient reconfiguration data generation algorithm is also built to take full advantage of our MORE architecture. The experimental results indicate that it can help reduce the reconfiguration cost by 37% on average.

A Novel High-Speed Multiplexing IC Based on Resonant Tunneling Diodes

A new multiplexing IC based on the resonant tunneling diode (RTD) is proposed. The unique negative differential resistance characteristics arising from quantum effects of the RTD enable us to develop a new functional low-power digital circuit. The proposed multiplexing IC consists of two current-mode-logic monostable-bistable transition logic elements (CML-MOBILEs) based on the RTD and a low-power selector circuit block. The proposed circuit has been fabricated by using an InP RTD/ heterojunction bipolar transistor monolithic microwave integrated circuit technology. The multiplexing operation of the fabricated quantum effect IC has been confirmed up to 45 Gb/s for the first time as a monolithic technology based on the quantum effect devices. The dc power consumption is only 23 mW, which is found to be one-fourth of the current state-of-the-art conventional transistor-based multiplexing IC.

Proposal for a digital converter of analog magnetic signals

A device which converts analog magnetic signals directly into digital information is proposed. The device concept is based on the monostable-bistable transition logic element, which consists of two resonant tunneling diodes (load and driver) connected in series and employs the monostable to bistable working point transition of the circuit. Using a magnetic resonant tunneling diode as the driver allows to control the resulting working point of the bistable region by an external magnetic field leading either to high or low output voltage of the circuit, effectively realizing what could be called digital magnetoresistance.

Experimental Demonstration of Ideal Noise Shaping in Resonant Tunneling Delta–Sigma Modulator for High Resolution, Wide Band Analog-to-Digital Converters

A ΔΣ modulator using a frequency modulation intermediate signal was demonstrated using a resonant tunneling logic gate called a monostable bistable transition logic element (MOBILE). This ΔΣ modulator is based on the nature of an FM signal and suitable for high-speed operation. Experiments using an InP-based MOBILE demonstrate good noise shaping characteristics. Moreover, the operation with a higher FM carrier frequency than the sampling frequency was demonstrated, showing equally good noise shaping performance. This makes the design of the voltage-controlled oscillator, which is a key component of the FM ΔΣ modulator, much easier. Consequently, an FM ΔΣ modulator using MOBILE is promising for high-resolution, wide-band analog-to-digital converters (ADCs).

Low-power static frequency divider using an InP-based monolithic RTD∕HBT technology

A low-power static frequency divider using an RTD/HBT MOnostable-Bistable transition Logic Element (MOBILE) scheme is proposed for the first time and operation of the circuit is demonstrated up to 20 GHz. The divided-by-two static frequency divider has been successfully implemented in an InP-based monolithic RTD/HBT IC technology. The number of devices used in the static frequency divider has been significantly reduced by using the proposed MOBILE scheme. The fabricated frequency divider operates at a clock frequency up to 20 GHz and dissipates d.c. power of 51 mW at a power supply of 3.3 V.

Resonant tunnelling delta sigma modulator suitable for high-speed operation

A resonant tunnelling logic gate, monostable-bistable transition logic element (MOBILE), was used to test high frequency operation of the ΔΣ modulator based on a frequency modulated intermediate signal. This ΔΣ modulator has no feedback loop and is promising for high-speed operation. Good noise shaping characteristics over four decades were measured. This ideal noise shaping demonstrated that the MOBILE can work as an ideal quantiser.

Room-temperature negative differential resistance in polymer tunnel diodes using a thin oxide layer and demonstration of threshold logic

Conjugated polymers, with π molecular orbitals delocalized along the polymer chain, are useful organic semiconductors that provide the possibility of molecular electronics for low-power organic-based memory and logic. Quantum functional devices based upon carrier tunneling processes open vistas into very efficient and low-power consumption circuitry that would be ideal for these applications. We demonstrate here strong room temperature negative differential resistance (NDR) for poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer tunnel diodes (PTD) using a thin TiO2 tunneling layer (∼2–8nm) sandwiched between the MEH-PPV and the indium tin oxide anode. A key advantage is the pronounced NDR using a thick polymer layer with a large active area, circumnavigating the need for molecularly-sized junctions. Current-voltage measurements show large and reproducible NDR with a PVCR as high as 53 at room temperature. We also demonstrate basic logic circuit operation using a pair of these PTDs connected in series to form a monostable-bistable transition logic element (MOBILE) latch.

Resonant Tunneling Diode/HBT D-Flip Flop ICs Using Current Mode Logic-Type Monostable-Bistable Transition Logic Element with Complementary Outputs

A current mode logic (CML)-type resonant tunneling diode (RTD)/heterojunction bipolar transistor (HBT) monostable-bistable transition logic element (MOBILE) IC with complementary outputs is proposed, which can simplify logic designs on the basis of complementary logic operation. Using the CML-type current modulator in the MOBILE IC, both the noninverted and inverted outputs are simultaneously generated with a single input signal. The CML-type MOBILE IC with complementary outputs has been fabricated using an InP-based RTD/HBT technology, and the operation of the fabricated circuit has been confirmed up to 10 Gb/s as a MOBILE with the complementary outputs. Moreover, the operation of a non-return-to-zero (NRZ) D-flip flop circuit, integrated with a set/reset latch (SR latch) using the CML-type complementary MOBILE IC has been for the first time confirmed up to 8 Gb/s with a low power consumption of 86 mW.

Monolithically integrated Si/SiGe resonant interband tunnel diode/CMOS demonstrating low voltage MOBILE operation

The first demonstration of the monolithic integration of CMOS and Si/SiGe resonant interband tunnel diodes (RITD) with negative differential resistance (NDR) is reported in this paper. The Si/SiGe RITDs exhibited a peak-to-valley current ratio (PVCR) up to 2.8 and peak current density ( J p) of 0.26 kA/cm 2 at room temperature. This study focused on the utilization of a pair of tunnel diodes connected in series to form a latch. Employing a FET to supply current into the latch, a RITD/NMOS monostable–bistable transition logic element (MOBILE) was realized. The latch exhibited a voltage swing of 84% at an applied supply voltage of 0.5 V. This logic element enables low voltage operation for high density circuit design of embedded memory.

Analysis of Transient Response and Operating Speed of MOBILE

To clarify the relationship between the figures-of-merit of resonant tunneling diodes and the operating speed of a monostable-bistable transition logic element (MOBILE), we investigated the transient response of a MOBILE using a simple current-voltage characteristics model. We found that an unstable point in a MOBILE affects its operation, and false operation occurs when the amplitude of the clock signal is inappropriate. From a calculation of transient time using peak-to-valley current ratio (PVR) and peak current density (j/sub P/) as parameters, we also discovered that a sufficiently high j/sub P/ and higher PVR (>6) are necessary for high-speed operations.

Experimental Demonstration of Capacitor-Coupled Resonant Tunneling Logic Gates for Ultra-short Gate-delay Operation

The capacitor-coupled monostable-bistable transition logic element (C2MOBILE) is an extension of the high-speed logic gate MOBILE based on the negative differential resistance of the resonant tunneling diodes. The C2MOBILE uses a transient current through the coupling capacitor to transmit signals between gates, and is expected to operate with an extremely short gate delay time. In this paper, basic operations of the C2MOBILE are demonstrated with the circuits fabricated on InP substrates. The circuits tested here are the 2- and 3-stage logic circuits and the AND/OR gate. The gate delay time was estimated to be around 1 ps for these circuits. A much shorter gate delay time close to 100 fs should be possible with the sophisticated circuit design and fabrication process.

Circuit and application aspects of tunnelling devices in a MOBILE configuration

AbstractIn this paper, circuit and application aspects of different monostable–bistable transition logic elements (MOBILEs) are analysed. By taking advantage of the multi‐state behaviour of resonant tunnelling devices (RTD) the logic depth and the circuit complexity per logic function is reduced at the gate level. Both, simulation and measurement results prove correct circuit operation in the gigahertz regime and I–O compatibiliy of the logic voltage levels. The scaling laws of the different MOBILEs are compared to each other in terms of speed and power dissipation. Detailed SPICE simulations based on experimental data precisely analyse the impact of fluctuations on the circuit functionality and performance. This study demonstrates that RTD‐based MOBILEs are ready for use in digital circuitry such as linear threshold gates which offer a highly reduced circuit complexity. Copyright © 2003 John Wiley & Sons, Ltd.

Nonvolatile reprogrammable logic elements using hybrid resonant tunneling diode–giant magnetoresistance circuits

We have combined resonant interband tunneling diodes (RITDs) with giant magnetoresistance (GMR) elements so that the GMR element controls the switching current and stable operating voltage points of the hybrid circuit. Parallel and series combinations demonstrate continuous or two-state tunability of the subsequent RITD-like current–voltage characteristic via the magnetic field response of the GMR element. Monostable–bistable transition logic element operation is demonstrated with a GMR/RITD circuit in both the dc limit and clocked operation. The output of such hybrid circuits is nonvolatile, reprogrammable, and multivalued.

A vertical resonant tunneling transistor for application in digital logic circuits

A vertical resonant tunneling transistor (VRTT) has been developed, its properties and its application in digital logic circuits based on the monostable-bistable transition logic element (MOBILE) principle are described. The device consists of a small mesa resonant tunneling diode (RTD) in the GaAs/AlAs material system surrounded by a Schottky gate. We obtain low peak voltages using InGaAs in the quantum well and the devices show an excellent peak current control by means of an applied gate voltage. A self latching inverter circuit has been fabricated using two VRTTs and the switching functionality was demonstrated at low frequencies.

Threshold logic circuit design of parallel adders using resonant tunneling devices

Resonant tunneling devices and circuit architectures based on monostable-bistable transition logic elements (MOBILEs) are promising candidates for future nanoscale integration. In this paper, the design of clocked MOBILE-type threshold logic gates and their application to arithmetic circuit components is investigated. The gates are composed of monolithically integrated resonant tunneling diodes and heterostructure field-effect transistors. Experimental results are presented for a programmable NAND/NOR gate. Design related aspects such as the impact of lateral device scaling on the circuit performance and a bit-level pipelined operation using a four phase clocking scheme are discussed. The increased computational functionality of threshold logic gates is exploited in two full adder designs having a minimal logic depth of two circuit stages. Due to the self-latching behavior the adder designs are ideally suited for an application in a bit-level pipelined ripple carry adder. To improve the speed a novel pipelined carry lookahead addition scheme for this logic family is proposed.