The model parameters of the BSIM4 model can be divided into several groups. The main model parameters are used to model the key physical effects in the DC and CV behavior of submicron MOS devices at room temperature. Here they are grouped into subsections related to the physical effects of the MOS transistor. The second group of parameters are the process related parameters.

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To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up. Zebang Guo. Cao, Xiaodong Jin, Jeff J.

Ou, Mansun Chan, Ali M. Weidong Liu, Synopsys Dr. Xiaodong Jin, Marvell Dr. Jeff J. Ou, Intel Dr. Partition of Igc Charge partitioning The continuous scaling of minimum feature size brought challenges to compact modeling in two ways: One is that to push the barriers in making transistors with shorter gate length, advanced process technologies are used such as non-uniform substrate doping. The second is its opportunities to RF applications. To meet these challenges, BSIM4 has the following major improvements and additions over BSIM3v3: 1 an accurate new model of the intrinsic input resistance for both RF, high-frequency analog and high-speed digital applications; 2 flexible substrate resistance network for RF modeling; 3 a new accurate channel thermal noise model and a noise partition model for the induced gate noise; 4 a non-quasi-static NQS model that is consistent with the Rg-based RF model and a consistent AC model that accounts for the NQS effect in both transconductances and capacitances.

Based on these parameters, the effect of effective gate oxide capacitance Coxeff on IV and CV is modeled [2]. It is worth pointing out that the new model parameters: the effective width Weffeot , length Leffeot , temperature Tempeot and bias condition Vddeot for EOT extraction are also needed in this calculation. Here, mtrlMod is a global selector which is used to turn on or off the new material models. This selector will be discussed in detail in Chapter 8.

Figure 1. Although this depletion layer is very thin due to the high doping concentration of the poly-silicon gate, its effect cannot be ignored since the gate oxide thickness is small. The depletion width in the poly gate is Xp. The depletion width in the substrate is Xd. The positive charge near the interface of the poly-silicon gate and the gate oxide is distributed over a finite depletion region with thickness Xp.

In the presence of the depletion region, the voltage drop across the gate oxide and the substrate will be reduced, because part of the gate voltage will be dropped across the depletion region in the gate. That means the effective gate voltage will be reduced. The device is in the strong inversion region.

The effective gate voltage can be calculated in the following manner. Assume the doping concentration in the poly gate is uniform. From 1. NF is the number of device fingers. The remaining terms in dW and dL are provided for the convenience of the user. They are meant to allow the user to model each parameter as a function of Wdrawn, Ldrawn and their product term.

By default, the above geometrical dependencies for dW and dL are turned off. Unlike the case of I-V, we assume that these dimensions are bias- dependent. The effective channel length Leff for the I-V model does not necessarily carry a physical meaning. It is just a parameter used in the I-V formulation. This Leff is therefore very sensitive to the I-V equations and also to the conduction characteristics of the LDD region relative to the channel region.

A device with a large Leff and a small parasitic resistance can have a similar current drive as another with a smaller Leff but larger Rds. The Lactive parameter extracted from capacitance is a closer representation of the metallurgical junction length physical length.

BSIM4 is its own valid designation limit which is larger than the warning limit, shown in following table. Equation 2. The zero-th and 1st moments of the vertical doping profile in 2. Combining 2. Appendix A lists the model selectors and parameters. Detail information on the doping profile is often available for predictive modeling. Therefore, as channel length becomes shorter, a Vth roll-up will usually result since the effective channel doping concentration gets higher, which changes the body bias effect as well.

Vth dependence on the body bias becomes weaker as channel length becomes shorter, because the body bias has weaker control of the depletion region. In BSIM4, the function form of 2. To model SCE, we use 0. This effect becomes very substantial as the channel width decreases and the depletion region underneath the fringing field becomes comparable to the "classical" depletion layer formed from the vertical field. The net result is an increase in Vth.

Vth change is given by TOXE 2. To do this we introduce the following 0. This is needed in order to set a low bound for the body bias during simulations since unreasonable values can occur during SPICE iterations if this expression is not introduced.

To account for the drain bias effect, The y dependence has to be included in 3. In subthreshold region, the channel charge density along the channel from source to drain can be written as BSIM4. In the model implementation, n of Vb is replaced by a typical constant value of 2. Experimental data shows that the subthreshold swing is a function of channel length and the interface state density.

Parameter CIT is the capacitance due to interface states. From 3. This tunneling happens between the gate and silicon beneath the gate oxide. To reduce the tunneling current, high-k dielectrics are being studied to replace gate oxide. In order to maintain a good interface with substrate, multi-layer dielectric stacks are being proposed.

The BSIM4 gate tunneling model has been shown to work for multi-layer gate stacks as well. The tunneling carriers can be either electrons or holes, or both, either from the conduction band or valence band, depending on the type of the gate and the bias regime. Figure 4. When the selectors are set to zero, no gate tunneling currents are modeled. This will cause Vth to vary along the channel. This effect is called bulk charge effect.

BSIM4 uses Abulk to model the bulk charge effect. Several model parameters are introduced to account for the channel length and width dependences and bias effects. Abulk is formulated by 5. The scattering mechanisms responsible for surface mobility basically include phonons, Coulombic scattering, and surface roughness.

For good quality interfaces, phonon scattering is generally the dominant scattering mechanism at room temperature. In general, mobility depends on many process parameters and bias conditions.

For example, mobility depends on the gate oxide thickness, substrate doping concentration, threshold voltage, gate and substrate voltages, etc.

BSIM4 keeps this option for the sake of simulation efficiency. Rs V and Rd V can be connected between the external and internal source and drain nodes, respectively; furthermore, Rs V does not have to be equal to Rd V. Considering only the channel current, the I-V curve can be divided into two parts: the linear region in which the current increases quickly with the drain voltage and the saturation region in which the drain current has a weaker dependence on the drain voltage.

The first order derivative reveals more detailed information about the physical mechanisms which are involved in the device operation. The first region is the triode or linear region in which carrier velocity is not saturated. The output resistance is very small because the drain current has a strong dependence on the drain voltage. The other three regions belong to the saturation region. As will be discussed later, there are several physical mechanisms which affect the output resistance in the saturation region: channel length modulation CLM , drain-induced barrier lowering DIBL , and the substrate current induced body effect SCBE.

These mechanisms all affect the output resistance in the saturation range, but each of them dominates in a specific region. The channel current is a function of the gate and drain voltage. But the current depends on the drain voltage weakly in the saturation region. When the threshold voltage is determined, the gate voltage is equal to the threshold voltage. But in the saturation region where the output resistance is modeled, the gate voltage is much larger than the threshold voltage.

Drain induced barrier lowering may not be the same at different gate bias. This will generate electron-hole pairs when these energetic electrons collide with silicon atoms. The substrate current Isub thus created during impact ionization will increase exponentially with the drain voltage. Isub affects the drain current in two ways. The total drain current will change because it is the sum of the channel current as well as the substrate current.

This is why SCBE is important for devices with high drain voltage bias. The Rout degradation factor F is given in 5.


BSIM 4.1.0 MOSFET Model-User's Manual






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