Development of tunnel diode devices and models for circuit design and characterization

Historically, the microelectronics industry has scaled down CMOS transistor dimensions in order to increase operating speeds, decrease cost per transistor, and free up on-chip real estate for additional chip functions. There are numerous challenges involved with scaling transistors down to the near term 32 nm node, and beyond. These challenges include short gate lengths, very thin gate oxides, short channel effects, quantum effects, band-to-band tunneling from source to drain, Gate Induced Drain Leakage, Fowler Nordheim tunneling, and increasing dopant concentrations. Field effect transistor circuits augmented with tunnel diodes lead to decreased circuit footprints, decreased device count, improved operating speeds, and lower power consumption without the need to solve current CMOS scaling challenges. Recently, N on P Si/SiGe resonant interband tunnel diodes (RITD) have been monolithically integrated with CMOS transistors. To further improve the benefits of RITD augmented circuits, P-on-N RITDS and all-Si RITDs were developed. Reported maximum peak to valley current ratios (PVCR), a key quantitative parameter of TDs, of 1.32 and 3.02 were measured, respectively. Since integrated circuits operate at elevated temperatures, the I-V characteristics of various TDs were measured at temperatures ranging from room temperature up to 200oC. Three figures of merit were extracted; (i) peak current density (JP), (ii) valley current density (JV), and (iii) PVCR. Normalizing over their respective values at room temperature allowed for direct comparison between the various TD structures. This method allowed the author to determine that all devices show a similar JP response. However, the Si/SiGe RITD structure was overall least sensitive to temperature variations. Furthermore, to design and optimize TD augmented circuits, a SPICE compatible model was developed. Past models have discontinuities, kinks in their slopes, difficult parameters to extract, unknown parameters, no closed form solutions, and/or poor fits to measured data. For this work a modified version of the S. M. Sze model with a superior match to experimental data, for Si based Esaki tunnel diodes (ETD) was developed. Using the developed model, several circuits were simulated, which were broken up into two groups. The first group of circuits is comprised of one TD and one of the following; (i) resistor, (ii) NMOS transistor, or (iii) TD. Finally, the behaviors learned from the simple circuits were used to simulate several TD augmented circuits such as (i) ADC comparator, (ii) TSRAM, (iii) and four basic logic gates

Simulation of double barrier resonant tunneling diodes

The double barrier resonant tunneling diode (DBRTD) is one of several devices currently being considered by the semiconductor industry as a replacement for conventional very large scale integrated (VLSI) circuit technology when the latter reaches its currently perceived scaling limits. The DBRTD was one of the first and remains one of the most promising devices to exhibit a room temperature negative differential resistance (NDR); this non-linear device characteristic has innovative circuit applications that will enable further downsizing. Due to the expense of fabricating such devices, however, it is necessary to extensively model them prior to fabrication and testing. Two techniques for modeling these devices are discussed, the Thomas-Fermi and Poisson-Schroedinger theories. The two techniques are then compared using a model currently under development by Texas Instruments, Incorporatedhttp://archive.org/details/simulationofdoub00portLieutenant, United States NavyApproved for public release; distribution is unlimited

Resonant tunnelling diode optoelectronic receivers and transmitters

This thesis describes the research work on double barrier quantum well (DBQW) resonant tunneling diode (RTD) based optoelectronic transmitters and receivers, focused on the design and characterization of resonant tunneling diode photodetectors (RTD-PD) implemented in the In53Ga47As/InP material system for operation at 1.55 μm and 1.31 μm wavelengths, and evaluate numerically the merits of the integration of an RTD/RTD-PD with a laser diode (LDs) to act as simple optoelectronic transmitters. The aim of the work was to investigate simple, low-cost, high-speed transmitter and receiver architectures taking advantage of RTDs properties such as the structural simplicity, high frequency (up to terahertz), and wide-bandwidth built-in electrical gain (roughly, from dc to terahertz). Also described are the preliminary studies of RTD-PDs operation as single photon detector at room temperature utilizing the excitability property. In this work, we evaluate which factors affect the bandwidth of RTD-PDs. Knowing the answer to this, we propose rules and optimizations necessary to achieving high bandwidth (>10 GHz) RTD-PDs. Furthermore, we show how to utilize the built-in amplification, arising from the RTD non-linear current-voltage (IV) curve and the presence of a negative differential resistance region (NDR) to building high responsivity photodetectors that can outperform current commercial technologies, particularly PIN photodiodes, in novel applications. The design and modeling work relied on numerical simulations utilizing the nonequilibrium Green’s function formalism (NEGF), which we implement using Silvaco ATLAS. We briefly introduce the NEGF method and Silvaco ATLAS and utilize them to do the design of the epitaxial structure of novel devices. The results of which are novel models which allow us to predict the effect that the RTD structural parameters (doping concentration and the lengths of both the emitter and collector) have on the peak voltage of the RTD. We study experimentally the factors affecting the bandwidth by optical characterization of several epitaxial layer stacks and propose hypotheses that help to explain the measured bandwidths. We show that for high-speed RTD-PDs (sub nanosecond), the light absorption layers should be confined to the locations where the electric field is sufficiently high and avoiding highly doped thick contact layers with band gap energies below the energy of the photons being detected. Additionally, we outline a set of rules for the design of RTD-PD detectors based on ni-n and p-i-n heterostructures, where the length, location, and doping level of the absorption regions are the relevant parameters to be considered in determining the bandwidth and responsivity of the devices. Moreover, we measure and report on the responsivity of RTDPDs under both DC and AC optical excitation. We show that RTD-PDs can have very high responsivity values reaching up to 1×107 A/W, and electrical bandwidth of around 1.26 GHz (1.75 GHz optical) that is limited by the lifetime of the photo-generated minority carriers (the holes). The last part of the thesis is dedicated to the study of RTD-PD circuits, where the integration between an RTD-PD and a laser diode (LD) is thoroughly examined. The LD acts as a load that is driven by the RTD-PD current. We derive and investigate the equivalent circuit for such a system incorporating the Schulman function for the RTD-PD IV, using the solution to study several operation regimes using MATLAB code. These regimes include the RTD-PD biased in the positive differential resistance region (PDR), when it is biased in the NDR region, and when induced to switch between the PDR and NDR regions. We also show how the excitability property of the RTD-PD can be used for detecting very low signal intensity levels, and the ability of RTDs to operate as voltage-controlled oscillators while biased in the NDR region

Theory and simulation of quantum photovoltaic devices based on the non-equilibrium Green's function formalism

This article reviews the application of the non-equilibrium Green's function formalism to the simulation of novel photovoltaic devices utilizing quantum confinement effects in low dimensional absorber structures. It covers well-known aspects of the fundamental NEGF theory for a system of interacting electrons, photons and phonons with relevance for the simulation of optoelectronic devices and introduces at the same time new approaches to the theoretical description of the elementary processes of photovoltaic device operation, such as photogeneration via coherent excitonic absorption, phonon-mediated indirect optical transitions or non-radiative recombination via defect states. While the description of the theoretical framework is kept as general as possible, two specific prototypical quantum photovoltaic devices, a single quantum well photodiode and a silicon-oxide based superlattice absorber, are used to illustrated the kind of unique insight that numerical simulations based on the theory are able to provide.Comment: 20 pages, 10 figures; invited review pape

무한한 상관길이를 가지는 위스너 수송 방정식의 결정론적 해

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2022. 8. 최우영.We propose a new discrete formulation of the Wigner transport equation (WTE) with infinite correlation length of potentials. Since the maximum correlation length is not limited to a finite value, there is no uncertainty in the simulation results, and Wigner-Weyl transformation is unitary in our expression. For general and efficient simulation, the WTE is solved self-consistently with the Poisson equation through the finite volume method and the fully coupled Newton-Raphson scheme. By applying the proposed model to resonant tunneling diodes and double gate MOSFET, transient and steady-state simulation results including scattering effects are shown.본 연구에서는 무한한 상관 길이를 가지는 위그너 수송 방정식의 새로운 수치해석적 풀이법을 제시하였다. 최대 상관 길이가 한정된 값으로 제한되지 않기 때문에, 시뮬레이션 결과에 불확실성이 발생하지 않으며, 제안된 표현법에서는 Wigner-Weyl 변환이 unitary하다. 일반적이고 효율적인 시뮬레이션을 위해, 위그너 수송 방정식을 푸아송 방정식과 유한 체적법과 뉴턴-랩슨 방식을 통해 self-consistent하게 풀었다. 제안된 모델을 resonant tunneling diode와 double gate MOSFET에 적용하여, 산란효과를 고려한 동적 그리고 정적 시뮬레이션 결과를 보여주었다.Chapter 1 Introduction 1 1-1 Various models for device simulation 1 1-2 Numerical problems in solving WTE 5 Chapter 2 Simulation methods 10 2-1 WTE with infinite correlation length 10 2-2 Numerical Methods 13 2-3 Multi-dimensional Simulation Methods 23 Chapter 3 Simulation methods 26 2-1 Simulation results according to the correlation length 26 2-2 Simulation for resonant tunneling diode 30 2-3 Simulation for double gate MOSFET 51 Chapter 4 Conclusion 70 Appendix 72 A-1 Numerical integration method of the nonlocal potential terms 72 A-2 2D electron density and electric potential results 75 A-3 Wigner function for each subband 78 References 85 Abstract 92박

Integrated micromachined quantum barrier mixers for high harmonic number millimeter wave receivers

This thesis presents the results of my endeavours at Leeds on research into subharmonic mixing employing double barrier resonant tunneling device (Quantum Barrier Device) at microwave and millimeter wave frequencies and an enabling technology for future improvement of the Quantum Barrier mixer. The research commenced with an empirical study of the electrical characteristics of a typical Quantum Barrier Device, and a model was developed to accurately simulate the discontinuities in the current-voltage characteristic as well as the capacitance-voltage behavior in the dc and the frequency domain. With a detailed analytical model, a general theory of subharmonic mixing was derived to demonstrate, with experimental proof, factors which favor the use of a Quantum Barrier Device as a mixing device at microwave frequencies, and to reveal any shortcomings. Measurements of a mixer at microwave frequencies and a harmonic multiplier at millimeter wave frequencies were also carried out, and presented with suggestions for possible improvements on the existing Quantum Barrier Device structure. In addition, several novel polymer-based micromachining technologies were developed for integration of these high frequency devices in the future, and presented in this thesis with S-parameter measurements. Particular reference was given to a handful of membrane-based micromachining technologies that enable a planar membrane-based printed circuit to be fabricated on a 5 micron thick polymer membrane in the absence of any steps involving thermal oxidation and low pressure chemical vapor deposition (LPCVD). The relatively low-cost low-temperature process uses a photosensitive resin (SU-8) to form a self-supporting membrane to which active devices can be mounted. Measured losses of transmission lines in these technologies are typically no more than 0.5 dB/cm at W-band, and this performance is comparable to the existing GaAs (or Silicon) membrane technologies

Reliable design of tunnel diode and resonant tunnelling diode based microwave sources

This thesis describes the reliable design of tunnel diode and resonant tunneling diode (RTD) oscillator circuits. The challenges of designing with tunnel diodes and RTDs are explained and new design approaches discussed. The challenges include eliminating DC instability, which often manifests itself as low frequency parasitic oscillations, and increasing the low output power of the oscillator circuits. To stabilise tunnelling devices, a common but sometimes ineffective approach is the use of a resistor of suitable value connected across the device. It is shown in this thesis that this resistor tunnel diode circuit can be described by the Van der Pol model. Based on this model, design equations have been derived which enable the design of current-voltage (I-V) measurement circuits that are free from both low frequency bias oscillations and high frequency parasitic oscillations. In the conventional setup, the I-V characteristic of the tunnelling device is extracted from the measurement by subtracting from the measured current the current through the stabilising resistance at each bias voltage. In this thesis, also using the Van der Pol model, a circuit for the direct measurement of I-V characteristics is proposed. This circuit utilises a series resistor-capacitor combination in parallel with the tunnelling device for stabilisation. Experimental results show that IV characterisation of tunnel diodes in the negative differential resistance (NDR) region free from oscillations can be made. A new test set-up suitable for radio frequency (RF) characterisation of tunnel diodes over the entire NDR region was also developed. Initial measurement results on a packaged tunnel diode indicate that accurate characterisation and subsequent small-signal equivalent circuit model extraction for the NDR region can be done. To address the limitations of low output power of tunnel diode or RTD oscillators, a new multiple device circuit topology, incorporating a novel design methodology for the DC bias decoupling circuit, has been developed. It is based on designing the oscillator specifically for sinusoidal oscillations, and not relaxation oscillations which are also possible in tunnel diode oscillators. The oscillator circuit can also be described by the Van der Pol model which provides theoretical predictions of the maximum inductance, in terms of the tunnel diode device parameters, that is required to resonate with the device capacitance for sinusoidal oscillations. Each of the tunnel diodes in the multiple device oscillator circuit is decoupled from the others at DC and so can be stabilised independently. The oscillator topology uses parallel resonance but with each tunnel diode individually biased and DC decoupled making it possible to employ several tunnel diodes for higher output power. This approach is expected to eliminate parasitic bias oscillations in tunnel diode oscillators whilst increasing the output power of a single oscillator. Simulation and experimental oscillator results were in good agreement, with a two-tunnel diode oscillator exhibiting approximately double the output power as compared to that of a single tunnel diode oscillator, i.e. 3 dB higher. Another method considered for the realisation of higher output power tunnel diode or RTD oscillators was series integration of the NDR devices. A new method to suppress DC instability of the NDR devices connected in series with all the devices biased in their NDR regions was investigated. It was successfully employed for DC characterisation with integrations of 2 and 5 tunnel diodes. Even though no suitable oscillator circuit topology and/or methodology with series-connected NDR devices could be established for single frequency oscillation, the achieved results indicated that this approach may be worthy of further investigation. The final aspect of this project focussed on the monolithic realisation of RTD oscillators. Monolithic oscillators in coplanar waveguide (CPW) technology were successfully fabricated and worked at a fundamental frequency of 17.5 GHz with -21.83 dBm output power. Finally, to assess the potential of RTD oscillators for high frequency signal generation, a theoretical analysis of output power of stabilised RTD oscillators was undertaken. This analysis suggests that it may be possible to realise RTD oscillators with high output power (0 dBm) at millimetre-wave and low terahertz (up to 1 THz) frequencies