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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 J. C. Tinoco and J.-P. Raskin Université catholique de Louvain Microwave Laboratory B-1348 Louvain-la-Neuve, Belgium RF Extraction Techniques for Series Resistances of MOSFETs
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 2 OUTLINE Introduction Bracale´s Method Bracale´s Modified Method Results Conclusions
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 3 INTRODUCTION Different methods have been developed to determine the extrinsic series resistances. They can be divided in two groups: DC and RF methods. DC MethodsRF Methods It is not possible to extract independently the drain and source resistances: R T = R d + R s It is not possible to determine the gate resistance. It is possible to extract independently the drain, source and gate resistances. Device biased under different conditions. Requires the equivalent circuit analysis.
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 4 INTRODUCTION The main RF methods are: Lovelace, Torres-Torres, Raskin and Bracale. Lovelace and Torres-Torres´ methods are quite sensitive to noise. Signal pre-treatments do not improve the extraction. Lovelace Torres-Torres
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 5 INTRODUCTION Bracale Raskin Raskin´s method also is quite sensitive to noise. Signal pre-treatments seem to improve the extraction. For deep-submicron devices its application seems limited. Bracale´s method is less sensitive to noise. Fails to determine the correct resistance values. Deep analysis is necessary for the Bracale´s method
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 6 Bracale´s Method Bias:V DS = 0 V & V GS >V T G mi → 0 Assumptions: Perfectly symmetric Device:C gsi = C gdi = C Constant mobility
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 7 INTRODUCTIONBracale´s Method Impedance Relationships:
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 8 Bracale´s Method Linear regression of the impedance relationship respect to the inverse of the gate overdrive. The intercept gives the corresponding series resistance.
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 9 Bracale´s Method Extraction MethodsR se R de R ge Classical Bracale7.57.32.8 Used in Simulations335 The extracted values differ from the values used in the simulations. It is necessary to review the assumptions made: Perfectly symmetric Device:C gsi = C gdi = C Constant mobility
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 10 Bracale´s Modified Method Mobility degradation coefficient: The inverse of the output conductance is a linear function of the inverse of the gate overdrive: The slope “s” and the intercept “b” are: And thus:
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 11 Bracale´s Modified Method The impedance relationships will be expressed as: They follow linear function respect to the inverse of the gate overdrive, the slope “x” will be: Extraction MethodsR se R de R ge Classical Bracale7.57.32.8 Mobility degradation included3.42.774.84 Used in Simulations335
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 12 Bracale´s Modified Method The mobility degradation strongly affects the extraction accuracy. Considering non-perfectly symmetry, the impedance relationships will be expressed as: Where k = C gs /C gd is called the asymmetry coefficient.
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 13 Bracale´s Modified Method Overcome the limitations of the classical method. Non-perfectly symmetry is considered. Mobility degradation coefficient is included (θ). Thus, the extracted series resistances will be obtained as: Extraction MethodsR se R de R ge Classical Bracale7.57.32.8 Mobility and asymmetry included33.24.85 Used in Simulations335
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 14 Bracale´s Modified Method Asymmetry coefficient: The imaginary part of the impedance parameters follow the next relationships: Thus, we can obtain k as:
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 15 Results ELDO software was used to simulate the S-Parameters of Partially- Depleted 0.13 µm SOI n-MOSFETs. The BSIM3SOI model from ST-Microelectronics was used. R se = R de = 3 & R ge = 5
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 16 Results = 0.6 R se = 3
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 17 Results R de = 3.2 R ge = 4.85 Extraction MethodsR se R de R ge Classical Bracale7.57.32.8 Mobility degradation included3.42.774.84 Mobility and asymmetry included33.24.85 Used in Simulations335
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J. C. Tinoco and J.-P. Raskin MOS-AK – 2008 18 Conclusions Original Bracale´s method does not allow accurate extraction of the series resistances. The main limitations of this method are: the carrier mobility degradation and transistor asymmetry. A new procedure was established, where the both effects are included. is obtained from DC output conductance measurements. k is obtained as the ratio of the imaginary part of Z- parameters. The new procedure allows to determine the correct resistance values.
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