Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and ....
outlined in the text book for the course: Operation and Modeling of The MOS.
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
EE 5121: MOS Transistor Modeling for Circuit Simulation Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations Study done and report prepared by: Nirav Desai ( 4280229 ) Department of Electrical and Computer Engineering, University of Minnesota Twin Cities
1 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Contents Introduction: Moderate Inversion MOSFET Models ..................................................................................... 3 BSIM3V3 Non-Quasi Static MOSFET Model: ................................................................................................. 4 BSIM3V3 MOSFET Model Fitting to LEVEL=3 HSPICE for simulations ...................................................... 4 AC Non-Quasi Static MOSFET Model: ....................................................................................................... 8 Transient Non-Quasi Static MOSFET Model: .......................................................................................... 10 BSIM3V3 Simulations from reference paper: Drain Current Spike............................................................. 11 BSIM3V3 Simulations from reference paper: Source Current Spike .......................................................... 12 BSIM3V3: 2 input NAND Gate: 1um & 0.18um channel lengths: ............................................................... 13 BSIM3V3: 2 input NOR Gate: 1um and 0.18um channel lengths ............................................................... 14 Conclusions ................................................................................................................................................. 15 References: ................................................................................................................................................. 16
2 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Introduction: Moderate Inversion MOSFET Models The original motivation for this project was to develop a moderate inversion model for the MOSFET that keeps track of the band bending beyond the onset of moderate inversion, at which the minority carrier concentration at the surface equals the bulk doping. This value of band bending is given by ( ) for an NMOSFET, Where, Na = Acceptor Doping in the Bulk, ni = Intrinsic Carrier Concentration, kT/q = Thermal Voltage = 26mV. Advanced surface potential based models, such as PSP [1] and Philips MOS Model 11 [2], track the surface potential very accurately and are thus very suitable for moderate inversion operation. Inversion charge (Qinv) based models such as BSIM3 [3] and BSIM4 have been designed specifically with moderate inversion and high frequency operation in mind and various corrections to the surface potential beyond the point of moderate inversion have been suggested which includes adding a constant 6kT/q to the surface potential at onset of strong inversion. A specific moderate inversion correction to the surface potential has been outlined in the text book for the course: Operation and Modeling of The MOS Transistor by Yannis Tsividis and is given by the following equations [4, Page 78, Second Edition Text Book]: ( )
(
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( )
( ) ( ) (
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All symbols follow the standard notation as outlined in the text book followed in the course: Operation and Modeling of the MOS Transistor: Yannis Tsivids (Third Edition.) The above model equations are missing in the Third Edition of the text book and have been adapted from the Second Edition.
3 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
BSIM3V3 Non-Quasi Static MOSFET Model: The second part of this project deals with MOSFET models for high frequency and pulsed operation of the MOSFET and is on the lines of the project proposal 2 outlined on class home page for Quasi Static MOSFET models. A study of simulations on the 2 input CMOS NOR and NAND gates is presented in subsequent sections. The BSIM3V3 Non Quasi Static MOSFET model is studied in this project and all simulations on the BSIM3V3 have been compared to LEVEL=3 HSPICE MOSFET model.
BSIM3V3 MOSFET Model Fitting to LEVEL=3 HSPICE for simulations The following plots show the model fit for LEVEL=49 (BSIM3V3) and LEVEL=3 (HSPICE) for models used in the subsequent simulations:
Fig 1: DC ID-VDS model match for LEVEL=49 (BSIM3V3) and LEVEL=3 (HSPICE) for a 20/1 dimension NMOS used in subsequent simulations.
4 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Figure 2: DC ID-VDS model match for LEVEL=49 (BSIM3V3) and N-Lumped LEVEL=3 (HSPICE) NMOS MOSFET models used in subsequent simulations. Dimensions for N=1 are 30/30.
5 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Fig 3: DC ID-VDS model match for LEVEL=49 (BSIM3V3) and LEVEL=3 (HSPICE) for 7.2/0.18 NMOS used in 2 input CMOS NAND gates.
6 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Fig 4: DC ID-VDS model match for LEVEL=49 (BSIM3V3) and LEVEL=3 (HSPICE) MOSFET models for 7.2/0.18 PMOS MOSFETs used in subsequent simulations. In all of the above graphs, the only parameter varied to achieve the match was the TOX for the LEVEL=3 HSPICE MOSFET model. The saturation region characteristics are an accurate match and linear region characteristics are not. This was picked as a trade-off as during pulsed operation, the MOSFET would most likely be in saturation for the entire transient.
The BSIM3V3 MOSFET model has 2 different Non-Quasi Static MOSFET models: AC Non-Quasi Static Model and Transient Non-Quasi Static MOSFET Model. All of the subsequent discussions are based on the reference: A Robust and Physical BSIM3 Non-Quasi-Static Transient and AC Small-Signal Model for Circuit Simulation by Mansun Chan, Kelvin Y. Hui, Chenming Hu and Ping K. Ko published in IEEE Transactions on Electron Devices, Vol. 45, No. 4, April 1998.
7 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
AC Non-Quasi Static MOSFET Model: Response to high frequency AC signals is modeled by enabling AC Non-Quasi Static Model which is a distributed channel model. This model breaks down the channel length internally into smaller sections so that transit time effects across each section are negligible. The figure below depicts the equivalent distributed model used in BSIM3V3:
Fig 5: Adapted from reference paper: Depicts the AC Non-Quasi-Static MOSFET model used in BSIM3V3 The specific model equations are: ( ) Relmore models the high frequency gm roll-off of the MOSFET.
8 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations An N-lumped model would give identical results asymptotically and the figures below depict the simulation results for using an N-lumped model versus the AC Non Quasi Static Model on BSIM3V3 (LEVEL = 49) enabled by specifying acnqsmod = 1 in the .model block of statements.
Fig 6: Frequency response for the gain of an NMOS inverter W/L=30/30 with 200kohms resistive load for BSIM3V3 Non-Quasi Static Model and N-Lumped LEVEL=3 HSPICE MOSFET model. Simulation adapted from reference paper.
9 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Transient Non-Quasi Static MOSFET Model: The transient Non-Quasi-Static MOSFET model on BSIM3V3 (LEVEL=49) is a charge deficit model, where the deficit charge is modeled by a Non-Quasi Static Charge with a relaxation time given by . This is an El-More Delay based model where the time constant τ is the relaxation time for the deficit charge. The specific model equations are: ( )
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Fig 7: Equivalent Circuit used for BSIM3V3 Non Quasi Static MOSFET Model enabled by specifying nqsmod=1 in .model block of statements. XD and XS is the charge partition ratio taken as 50-50 in the simulations. Quasi-Static approaches to deal with the transient currents are to allocate the channel charge to source and drain in different ratios 40%-60% or 10%-90%. This approach allocates the charge Qcheq(t) in these ratios instantaneously at time t and this leads to current spikes at source and drain nodes. The Non-Quasi-Static approach avoids these current spikes and gives more realistic rise and fall times at the associated nodes. The following sections describe the simulations carried out to study these effects.
10 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
BSIM3V3 Simulations from reference paper: Drain Current Spike
Fig 8: Drain current of the NMOSFET during turn-on transient simulated using LEVEL=3 HSPICE and LEVEL=49 BSIM3V3. Input step had a 1ps rise time. Self loading of the transistor limits the output rise time. The blue line is for Non-Quasi-Static Model and green is for Quasi-Static model with XQC=0.1. The labeling in figure is wrong. Quasi Static models give current spikes of varying magnitudes depending on the charge partitioning ratio leading to faster rise times at output nodes. Simulation adapted from reference paper.
11 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
BSIM3V3 Simulations from reference paper: Source Current Spike
Fig 9: This figure demonstrates the source current spike during the turn-off transient for the Quasi-Static Model with XQC = 0.4 and 0.1 and for Non-Quasi Static Model with XPART = 0.5. The source current spike leads to faster fall times at output for Quasi Static MOSFET models. Simulation adapted from reference paper.
12 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
BSIM3V3: 2 input NAND Gate: 1um & 0.18um channel lengths:
Fig 10: Output node voltages and currents for a 2 input NAND gate simulated using Quasi-Static Model with XQC=0.4 and 0.1 and Non-Quasi-Static MOSFET MODEL with XPART=0.5. The current spikes for Quasi-Static models give faster rise and fall times. All transistors are 7.2/0.18.
Fig 11: Same simulations as above this time with channel lengths of 1um. Widths changed appropriately. 13 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
BSIM3V3: 2 input NOR Gate: 1um and 0.18um channel lengths
Fig 12: Output node voltages and currents for a 2 input NOR gate simulated using Quasi-Static Model with XQC=0.4 and 0.1 and Non-Quasi-Static MOSFET MODEL with XPART=0.5. The current spikes for Quasi-Static models give faster rise and fall times. NMOS size: 7.2/0.18 PMOS size: 28.8/0.18 Output node voltages are not identical for Quasi-Static and Non-Quasi-Static Models. The figure also depicts the intermediate node voltage for the series connection of 2 PMOS transistors in VINT..
Fig 13: Same simulations as above with NMOS channel length = 1um. The output node voltages are now identical for Quasi-Static and Non-Quasi-Static models unlike the previous case. 14 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
Conclusions A study of the Non-Quasi Static BSIM3V3 MOSFET model was carried out. The reference paper was used as a template to understand the model and to learn to do simulations using the model. All simulations from the reference paper could not be reproduced. However, important transient and ac simulations could be replicated and are outlined in this report. All simulations outlined in the reference paper use NMOSFETS with channel lengths larger than 1um. There is no reference point for sub-micron channel length MOSFETs in the reference paper. Simulations for 2 input NOR gate depict an inaccuracy in the final voltage level at output for 0.18um channel length MOSFETs. Simulations for 2 input NAND and NOR gates with channel lengths greater than 1um show accurate voltage levels at output. However, they depict significant current spikes which cannot be explained. There are known inaccuracies in the BSIM3V3 Non-Quasi-Static MOSFET model as outlined in [6.] Also current spikes in Quasi-Static MOSFET models lead to faster rise and fall times at the output as compared to Non-Quasi-Static MOSFET models.
15 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
Final Project Report: BSIM3V3 Non Quasi Static MOSFET Model: Study and Simulations
References: 1. PSP: An Advanced Surface-Potential-Based MOSFET Model for Circuit Simulation Gennady Gildenblat, Xin Li, Weimin Wu, Hailing Wang, Amit Jha, Ronald van Langevelde, Geert D. J. Smit, Andries J. Scholten, and Dirk B. M. Klaassen IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 53, NO. 9, SEPTEMBER 2006 2. PHILIPS MOS MODEL 11: http://www.nxp.com/wcm_documents/models/mos-models/model-11/rvl141200.pdf 3. BSIM3: A Physical and Scalable I-V Model in BSIM3V3 for Analog/Digital Circuit Simulation Yuhua Cheng, Min-Chie Jeng, Zhihong Liu, Jianhui Huang, Mansun Chan, Kai Chen, Ping Keung Ko, Chenming Hu IEEE Transactions on Electron Devices, Vol. 44, No. 2, February 1997 4. AN EXPLICIT PHYSICAL MODEL FOR THE LONG-CHANNEL MOS TRANSISTOR INCLUDING SMALL-SIGNAL PARAMETERS ANA ISABELA, ARAUJO CUNHA, MARCIO CHEREM SCHNEIDER and CARLOS GALUPMONTORO Departamento de Engenharia ElCtrica, Universidade Federal de Santa Catarina, C.P. 476, CEP 88040-900, Florianbpohs. SC, Brazil Solid-State Electronics~ Vol. 38, No. I I, pp. 1945-1952, 1995 5. A Robust and Physical BSIM3 Non-Quasi-Static Transient and AC Small-Signal Model for Circuit Simulation by Mansun Chan, Kelvin Y. Hui, Chenming Hu and Ping K. Ko, IEEE Transactions on Electron Devices, Vol. 45, No. 4, April 1998. 6. A New Approach to Model Nonquasi-Static (NQS) Effects for MOSFETs—Part I: Large-Signal Analysis Ananda S. Roy, Juzer M. Vasi, Senior Member, IEEE, and Mahesh B. Patil IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 50, NO. 12, DECEMBER 2003
16 Nirav Desai ( 4280229 ) Dept. of ECE, University of Minnesota, Twin Cities
