The shifted-rectangle approximation for simplifying the analysis of ion-implanted MOSFETs and MESFETs
TL;DR: In this article, a shifted-rectangle approximation (SRA) was proposed to obtain a quadratic function of the gate controlled depletion charge for the V d -Q d characteristics of implanted FETs.
Abstract: The ability to express the depletion layer voltage drop V d in terms of a quadratic function of the gate controlled depletion charge Q d is shown to be a key to the success of analytical modelling of ion-implanted MOSFETs and MESFETs. It is shown that such a quadratic function for the V d - Q d characteristics of implanted FETs can be obtained by approximating the implanted doping profile by a “shifted-rectangle” profile whose parameters can be derived directly from implantation parameters. It is also shown that the shifted-rectangle approximation (SRA) is not just an artifice for simplicity but accurately conserves the actual Q d , V d and depletion width conditions of both shallow and deep implanted Gaussian shaped doping profiles. The SRA simplifies the analysis of multiple-implanted devices and can be considered to be a basic approximation to be used along with the depletion and gradual channel approximations for a simple and accurate analysis of the non-uniformly doped FETs.
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TL;DR: In this paper, a conformal mapping technique is used to analytically solve the two-dimensional Poisson equation, whereby inhomogeneous substrate doping is taken into account, for the geometry and voltage dependence of threshold voltage and for the subthreshold behavior of short-channel MOSFETs.
Abstract: In this paper we present a new theoretical approach in MOS modeling to derive analytical, physics-based model equations for the geometry and voltage dependence of threshold voltage and for the subthreshold behavior of short-channel MOSFETs. Our approach uses conformal mapping techniques to analytically solve the two-dimensional Poisson equation, whereby inhomogeneous substrate doping is taken into account. The presented model consists of analytical equations in closed form and uses only physically meaningful parameters. Therefore, the results are not only useful in circuit simulators but also in calculations of scaling behavior, where planned processes can be investigated. Comparison with numerical device simulation results and measurements confirm the high accuracy of the presented model.
71 citations
TL;DR: PREDICTMOS-a predictive compact model for structure oriented simulation of MOS devices is presented which has been developed by use of strongly physics-based model equations for threshold voltage, surface potential in weak inversion, and currents in strong inversion including the saturation regime.
Abstract: In circuit design and device scaling investigations, there is still a demand for improved analytical models of MOSFETs with less fitting parameters and a good scalability. In this paper, PREDICTMOS-a predictive compact model for structure oriented simulation of MOS devices is presented which has been developed by use of strongly physics-based model equations. For threshold voltage, surface potential in weak inversion, and currents in strong inversion including the saturation regime, the equations have been derived using our recently published conformal mapping techniques for solving the two-dimensional Poisson equation, and a new way to solve the transistor current differential equation. They make use of real structural parameters without any need of physically meaningless fitting parameters. This results in a strong link between electrical parameters and the process and layout data of the device and an excellent scalability while keeping physical insight. PREDICTMOS has been implemented in the ELDO circuit simulator. Its results in comparison with numerical device simulations and measurements show good agreement down to dimensions of 0.1 μm .
14 citations
TL;DR: In this article, it was shown that the behavior of the charge and position of the 2-DEG as a function of gate-source and drain-source voltages can be regarded as a simple buried-channel (BC) MOSFET.
Abstract: It is shown that, from the point of view of the behavior of the charge and position of the Two-Dimensional Electron Gas (2-DEG) as a function of gate-source and drain-source voltages, the complex High Electron Mobility Transistor (HEMT) can be regarded as a simple Buried-Channel (BC) MOSFET. Thus, the characteristics of a HEMT, namely channel charge and capacitance/transconductance as a function of gate voltage below and above threshold are akin those of a BC MOSFET. Hence, there are discrepancies in the conventional Surface Channel MOSFET-like approach to HEMT modeling. Existing simple BC MOSFET dc and ac models can be used for on-paper analysis and computer aided simulation of HEMT devices and circuits, if the HEMT is represented by an equivalent BC MOSFET as derived in this paper. The new representation can be useful for modeling of short-channel HEMT phenomena.
12 citations
01 Jan 1995
TL;DR: In this paper, a physics-based, compact model for the threshold voltage shift in short-channel MOSFETs is presented, which is based upon a new theoretical approach in MOS modeling.
Abstract: In this paper we present a physics-based, compact model for the threshold voltage shift in short-channel MOSFET’s, which is based upon a new theoretical approach in MOS modeling. This method uses conformai mapping techniques to solve the 2D Poisson equation in the space charge region underneath the gate and considers inhomogeneous doping profiles therein. The derived model equations appear in closed form and require only two physical fitting parameters related to a geometry and a doping approximation. A comparison with numerical device simulations reveals a high degree of accurateness down to channel lengths of 0.2µm.
2 citations
01 Jan 1996
TL;DR: In this article, the feasibility for developing imagers in Sic through the fabrication and demonstration of a buried channel CCD linear shift array was investigated, and the MOS field effect family was studied.
Abstract: Silicon carbide is a wide bandgap semiconductor that is well suited for high power, high temperature electronic devices due to its remarkable electronic and thermal properties Photosensitive devices in the 6H polytype of Sic have also been demonstrated, showing high sensitivity in ultraviolet wavelengths near 270 nm Furthermore, the native oxide on Sic is silicon dioxide, meaning that SIC can be thermally oxidized to form a high quality gate dielectric, making metal-oxide-semiconductor (MOS) devices possible These qualities make silicon carbide ideal for constructing UV sensitive CCD imagers 'This work investigates the feasibility for developing imagers in Sic through the fabrication and demonstration of a buried channel CCD linear shift array Several elements of the MOS field effect family were studied With careful surface preparation and device processing techniques, SiC/silicondioxide interfaces have been ameliorated to achieve surface state densities below 2e l1 per-centimeters-squared and electron surface mobilities above 40 centimeters-squared-per-volt-second Buried channel MOSFETs were fabricated with ion implantation of nitrogen at elevated temperatures and have functioned with electron mobilities in excess of 180 centimeters-squared-pervolt-second, which shows an advantage of using the buried channel structure Studies of capacitance characteristics of the buried channel devices hold good agreement with a general one-dimensional depletion model A double polysilicon level, overlapping gate process was adapted to the SiC/MOS system A four phase buried channel CCD shift register was built and operated in ,the pseudo-two phase configuration at room temperature Device clocking frequencies were limited to 30 kHz by slow charge readout techniques, but higher speeds have been estimated In this frequency range, charge transfer efficiencies were probably dominated by carrier trapping in bulk states, which may be present due to ion implantation Recommendations for improvement of device performance and methods of integrating the CCD with UV photodetectors are given
2 citations
Cites methods from "The shifted-rectangle approximation..."
...In order to better utilize the simpler model, device researchers have even tailored multiple implants to make the resulting profile as rectangular as possible [83], [84]....
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References
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TL;DR: In this paper, analytical forms for the buried-channel CCD and its counterpart the buried channel MOSFET having Gaussian impurity charge profiles were developed for describing all important potentials, charges, distances, and currents in terms of the profile structural parameters.
Abstract: Analytical forms are developed for the buried-channel CCD and its counterpart the buried-channel MOSFET having Gaussian impurity charge profiles. The results are able to describe all important potentials, charges, distances, and currents in terms of the profile structural parameters. The model will be quite useful in the design of buried-channel circuits for VLSI applications where it is expected that highly nonlinear profiles will be obtained by the use of very shallow ion implants and minimal high-temperature processing.
21 citations
TL;DR: In this article, a semi-empirical modification of a closed form expression for the inversion charge is presented to calculate the extrapolated threshold voltage versus source-substrate bias in nonuniformly doped MOSFET's.
Abstract: A simple algorithm is presented that is based on a semi-empirical modification of a closed form expression for the inversion charge, to allow the calculation of the so-called extrapolated threshold voltage versus source-substrate bias in nonuniformly doped MOSFET's. This algorithm is suitable for incorporation into process simulation computer programs like SUPREM. It is demonstrated, by comparison to exact calculations and to measurements, that the algorithm gives accurate values of extrapolated threshold voltage even for cases where junctions are present in the MOSFET substrate under the gate.
20 citations
TL;DR: In this article, an analytical mobility model for the I-V characteristics of n-channel enhancement-mode MOSFETs, in which the effects of the two-dimensional electric fields in the surface inversion channel and the parasitic resistances due to contact and interconnection are included.
Abstract: In this paper we develop an analytical mobility model for the I–V characteristics of n-channel enhancement-mode MOSFETs, in which the effects of the two-dimensional electric fields in the surface inversion channel and the parasitic resistances due to contact and interconnection are included. Most importantly, the developed mobility model easily takes the device structure and process into consideration. In order to demonstrate the capabilities of the developed model, the structure- and process-oriented parameters in the present mobility model are calculated explicitly for an n-channel enhancement-mode MOSFET with single-channel boron implantation. Moreover, n-channel MOSFETs with different channel lengths fabricated in a production line by using a set of test keys have been characterized and the measured mobilities have been compared to the model. Excellent agreement has been obtained for all ranges of the fabricated channel lengths, which strongly support the accuracy of the model.
19 citations
TL;DR: In this article, the Gaussian-implanted profile of buried layers can be represented by an equivalent box and the average doping and the depth of this box can be obtained directly from a knowledge of the implantation parameters.
Abstract: From the charge-voltage considerations, it is shown that the Gaussian-implanted profile of buried layers can be correctly represented by an equivalent box. The paper also shows that the average doping and the depth of this box can be obtained directly from a knowledge of the implantation parameters.
15 citations
TL;DR: In this paper, the field effect mobilities of n-channel depletion-type MOS transistors were measured, comparing transistor G{m} - V{g} and diode C - V_{g} characteristics.
Abstract: It is found that surface electron mobility can exceed electron mobility in bulk. Field-effect mobilities of n-channel depletion-type MOS transistors were measured, comparing transistor G_{m} - V_{g} and diode C - V_{g} characteristics. Electron mobility in a highly doped n-type channel layer exceeds that in bulk at around the onset of surface accumulation. This can be explained by reduction in ionized impurity scattering under accumulation conditions. In accumulation conditions, excessive electrons screen the Coulombic field from ionized impurities. This is confirmed by theoretical calculation based on the Maxwell-Boltzmann distribution of electrons and electron-concentration-dependent electron mobility.
14 citations