Introduction
Terahertz and Application
Terahertz is the frequency resource ranging from 100 GHz to 10 THz band, the wavelength is 0.1 mm to 1 mm (sub-millimeter wave) located in the middle region of the electromagnetic wave and infrared wave of the electromagnetic spectrum (Fig. 1- 1). Field research was carried out less than in other frequency bands, it is called "terahertz gap" in the sense of empty frequency bands. To overcome the operating THz regime by using plasma wave transistor (PWT) [12][13] using a plasma wave which is.
By using the plasma resonance phenomenon with 2D channel electron density operating in a high frequency region which is able to cut off the frequency of the transistor. Application of terahertz technology divided into three areas, imaging, spectroscopy and wireless communication has been active in the research field.
Terahertz Detector
- Plasma Wave FET Theory
- Terahertz Detector Operating Principle
The channel length is very short 2D electron gas (2DEG) under the transfer of electrons on the FET channel, can be expressed by hydrodynamic equation (Equation 1.1), continuity equation (Equation 1.2) instead of the motion of the particles of electrons and a hydrodynamic wave equation in shallow water that are interpreted as similar[12]. The plasma wave speed is proportional to the electron carrier density of the channel, the capacitance between gate and channel. When satisfied with asymmetric boundary conditions between the source and the drain (Eq) The flow of the wave in the channel is unstable, due to amplification of the wave by continuous reflection between the source drain, causing plasma wave oscillation.
To analyze the nonlinear characteristic of the plasma wave by 2DEG channel for detection and mixing of the THz wave and treat the plasma resonance and non-resonance operating region from the dispersion transmission line. The operating range of the PWT can be in two ranges according to the operating frequency, and the dependence of the operating range on the gate length is shown in Fig. In this case, kinetic inductance of Fig. 1-6(b) is a very important factor in determining the resonant condition.
In Figure 1.6(a), the plasma wave is repeatedly reflected at the boundary of the source and drain channels, creating a large amplitude standing wave. The plasma waves generated at the source will decay before reaching the drain, so the alternating current will only exist in a small part of the channel next to the source. Here the resistance of the entire MOSFET channel is 𝐿𝜌/𝑊, the total capacitance is CWL (W is the gate width, 𝜌 is the channel resistance), the time constant is τ𝑅𝐶 = 𝐿2𝜌𝐶.
If the conditions of case 1-a are met, the operation of the detector will be resonant, which corresponds to the excitation of discrete modes of plasma oscillations in the channel. 1-b, 2-b mode of operation, regardless of ωτ, if the ac current generated in the input signal cannot reach the drain, the output voltage can be simplified to. U Where v0 is the time average value of the electron velocity and U0 is the time average value of the channel potential, and the term vn and Un vary with time and frequency nω, where ω is the incident frequency of the detector.
Motivation
Thesis Overview
Contour plot of channel electron density modulation along with channel position at the same gate drive voltage Vg - Vth = 0.1 and each gate incident frequency (a) 6 GHz, (b) 60 GHz, (c) 600 GHz. For e(Ug-Uth)>>𝜂kBt (𝜂 is the transport ideality factor in the channel) the plasma wave transition time equation [38]. And consider the fluctuation of terahertz entering the gate, it is shown that in the terahertz regime, the non-quasi-static simulation is suitable for the simulation in Table 1.
2-4 shows the transient simulation of mixed-mode TCAD [38] by adding a different external capacitance between the gate and the drain, because the asymmetric environment between the source and the drain is necessary for the extraction △u in the non-resonant THz detector based on How. MOSFETs [40][41]. Asymmetric boundary condition applied to transient simulation of mixed-mode TCAD frame (Fig. 2-1) by adding different external capacitance between gate and drain. Contour plots of channel electron density modulation along with channel position at each time scale.
For the rigorous description of plasma wave decay and propagation in the channel region, the numerical solution of the continuity equation Eq. 2-8 shows the transient simulation of the mixed-mode SPICE [38] by adding varied external capacitance between gate and drain, for asymmetry boundary condition environment between source and drain for extracting △u in non-resonant THz detector based on Si MOSFET [ 40][41]. The applied asymmetric boundary condition in the transient simulation of the mixed-mode SPICE framework (Fig. 2-8) by adding varied external capacitance between gate and drain.
SPICE simulation results of photoreaction as a function of gate voltage (a) Quasi-static model, (b) Non-quasi-static model. Contour plots of channel density modulation along with channel position at the same gate crossover voltage Vg - Vth. The resulting MOSFET physics variation (thin oxide, gate length) shows the following equation.
Modeling and Simulation of Terahertz Detector…
Modeling Terahertz Detector
- Quasi Static, Non Quasi Static
- TCAD Modeling (Boundary Condition)
- Quasi Plasma 2DEG
- SPICE Modeling (Boundary Condition)
- SPICE Modeling (Non Quasi Static)
For accurate simulation and analysis of MOSFET operation, partial differential equations of the continuity equation for time and space can be solved numerically. In general, there is a physical value analysis of time that takes place in two ways. In this simulation, the results show that in the low-frequency regime in 6 GHz, the shape of the electron modulation shows that the electron responds immediately to the signal variation, but consider that the high-frequency regime in 600 GHz electron modulation cannot respond to the signal variation.
If the condition is met that the plasma wave transit time 𝜏𝑡𝑝𝑙 through the channel is much shorter than the oscillation period of the radiation field. Uth is the threshold voltage of the MOSFET, Ug is the gate voltage, L is the channel length of the transistor. The results of the comparison are shown in the table. Figure 2-5 shows that the modulation of the 2DEG channel density in a 0.7 THz transient simulation has been demonstrated with a TCAD framework based on the coupled Drude and continuity equation with a normal electric field-dependent mobility model.
These contour plots of the channel 2DEG density (at tox = 1.1 nm) modulation along with the channel position on each time scale depend on the symmetry. Regarding the symmetrical condition, it is equal to the propagation distance at the source and drain side. However, in the non-resonant detection mode (ωτ < 1), the plasma waves of 2DEG cannot exist in the channel due to overdamping, which means a longer propagation length than the coherent distance, thus ultimately giving rise to asymmetric channel electron distribution along the channel length direction [13] .
2-7 we modeled the quasi-plasma electron box based on the assumption of 'quasi-static' 2DEG plasma density for the resulting channel electron distribution with asymmetry during the exposure to THz radiation. Although the resulting 2DEG behavior must be described by the hydrodynamic Euler equation with the convection component in the strict way, the quasi-plasma 2DEG modeling has been performed on the basis of the TCAD platform [39], which does not include the hydrodynamic Euler formalism, for efficient simulation of non-resonant broadband THz detectors by taking advantage of well-established MOSFET models and the DC/AC analysis environment at TCAD. Quasi plasma 2DEG length is determined by, electron modulation simulation TCAD frame work and extract max length of source side length,.
The scheme of the applied asymmetric boundary condition in the transient simulation of the mixed-mode SPICE framework by adding varied external capacitance between gate and drain (Lg= 300 nm, tox= 1.1 nm, Vth= 0.2V). And all parasitic elements are substitute passive elements, that is the other difficulty of the model [51].
Simulation Results of Terahertz Detector
- TCAD,SPICE Simulation Results
- Physical Validity of NQS model
- Noise Equivalent Power
In the case of the ultra-thin gate dielectric, the electron density is sensitive as the gate bias voltage. The propagation distance from the 2DEG density simulation results is reduced by reducing the tox, since the modulation and propagation of an electron liquid of plasma waves (l=s(τ/ω)0.5) definitely depends on the plasmon decay time τ=μm/e where 𝜇 is the carrier mobility, m is the effective mass of the electron, the parameter 𝜏 is the quality factor. The simulation results as a function of the gate voltage according to the variation of the tox and the 4 nm spice simulation results.
The definition is, what is the incident power (sometimes for a frequency range) that produces a detector response equal to the noise voltage at the output of the device. In this thesis, I have reviewed the state of the art in terahertz detectors and set benchmarks for competitive performances, discussed the operation of terahertz response plasma wave device models based on existing theory. The period of the oscillations is smaller than the transit time of the plasma waves that we need for non-quasi-static analysis.
The solution of the non-quasi-static modeling we use the quasi-plasma 2DEG in TCAD platform, SPICE modeling uses new Elmore model for non-quasi-static modeling. In bearing capacitor is the weakening of the drain side signal which makes the AC short the drain side, and charge asymmetry in the source and drain. The block diagram terahertz chip board cannot operate all the terahertz at the same time.
Future work applies to the THz detector compact model in the simulation, we can predict the whole system response and the design concept is optimized. Terahertz plasma wave resonance of two-dimensional electrons in high electron mobility InGaP∕ InGaAs∕ GaAs transistors. Principles of Terahertz Science and Technology: Proceedings of the International Conference, held in Mainz, Germany, June Vol. 170).
Rational design of high-responsivity detectors of terahertz radiation based on distributed self-mixing in silicon field-effect transistors. Plasmonic terahertz wave detector based on silicon field-effect transistors with asymmetric source and drain structures.
Summary & Conclusion
Future Works
![Figure 1-5. Schematics of a FET as a THz detector (a) and the equivalent circuit resonant detector (b), non-resonant detector(c) [1]](https://thumb-ap.123doks.com/thumbv2/123dokinfo/10541722.0/18.893.138.756.132.389/figure-schematics-detector-equivalent-resonant-detector-resonant-detector.webp)
