FinFET Mismatch in Subthreshold Region: Theory and Experiments

In this paper, we study the drain-current mismatch of FinFETs in subthreshold, from both modeling and experimental point of view. We propose a simple model that takes into account the effect of threshold voltage and subthreshold swing fluctuations and their correlation. For long-channel devices (longer than a critical length LC), characterized by a subthreshold swing close to the ideal value, the overall current mismatch is dominated by threshold voltage fluctuations and, therefore, is gate voltage independent. The subthreshold swing fluctuations give a negligible effect on the drain-current mismatch and are uncorrelated with the threshold voltage fluctuations. For short-channel devices (shorter than a critical length LC), characterized by a strong dependence of subthreshold swing on the channel length, the overall current mismatch presents an additional relevant contribution associated with the subthreshold swing fluctuations. This component depends on the gate voltage overdrive and is ascribed to the gate line edge roughness, resulting in a partial correlation between threshold voltage and subthreshold swing fluctuations

FinFET Mismatch in Subthreshold Region: Theory and Experiments

In this paper, we study the drain-current mismatch of FinFETs in subthreshold, from both modeling and experimental point of view. We propose a simple model that takes into account the effect of threshold voltage and subthreshold swing fluctuations and their correlation. For long-channel devices (longer than a critical length LC), characterized by a subthreshold swing close to the ideal value, the overall current mismatch is dominated by threshold voltage fluctuations and, therefore, is gate voltage independent. The subthreshold swing fluctuations give a negligible effect on the drain-current mismatch and are uncorrelated with the threshold voltage fluctuations. For short-channel devices (shorter than a critical length LC), characterized by a strong dependence of subthreshold swing on the channel length, the overall current mismatch presents an additional relevant contribution associated with the subthreshold swing fluctuations. This component depends on the gate voltage overdrive and is ascribed to the gate line edge roughness, resulting in a partial correlation between threshold voltage and subthreshold swing fluctuations

Effects of midline thoracotomy on pulse pressure variations during pressure-control ventilation

Objective During mechanical ventilation, the heart–lung interaction induces a cyclic oscillation of the arterial pulse pressure. The measure of this respiratory changes, called pulse pressure variation (PPV), is one of the most reliable index of fluid responsiveness. It is used as a functional hemodynamic monitoring in several conditions (general anesthesia, sepsis, ALI/ARDS). During cardiac surgery, midline thoracotomy significantly alters heart–lung interaction and, consequently, PPV. The aim of the study was the evaluation of the effects of sternotomy on PPV during pressure-control ventilation (PCV). Methods Nineteen patients (age 62 ± 10 years) undergoing elective CABG in a tertiary university hospital were enrolled. A Swan–Ganz catheter, an arterial catheter and a central venous catheter was inserted in order to collect pressure waveforms. After the induction of general anesthesia all the patients were mechanically ventilated (PCV), setting pressure values in order to obtain a tidal volume of 8 ml/kg. Hemodynamic data were collected 5 min before and after sternotomy. PPV was calculated offline from the collected waveforms, according to the formula reported by Michard and colleagues [1]. Results The PPV, cardiac index, stroke volume, mean arterial pressure, airway pressure and tidal volume did not change after sternotomy. We subsequently differentiated patients according to PPV values (Fig. 1). In the subgroup of patients with PPV > 13% (7/19 patients), we found a good correlation between PPV and Paw (Pearson correlation 0.861 P = 0.03; R2 = 0.74 P = 0.049); after sternotomy, PPV was significantly reduced (15.4 ± 2.8% vs 8.2 ± 1.6%, P = 0.043) and it was no more correlated with Paw. In the subgroup of patients with PPV < 13% (12/19 patients), we did not find any correlation between PPV and Paw, and sternotomy had no effects on hemodynamic data. Conclusions During PCV, airway pressure affects PPV only when patients are in a ‘fluid responsive’ status (PPV > 13%); similarly, sternotomy reduces PPV only when baseline is above the hreshold value of 13%. It may thus be possible that midline thoracotomy makes a ‘fluid responsive’ patient unresponsive to a fluid challenge by leading his heart to work on the plateau portion of theFrank–Starling curve. This hypothesis would be confirmed by the lack of correlation between airway pressure and PPV after opening the thorax. Reference 1. Michard F, Boussat S, Chemla D, et al.: Am J Respir Crit Care Med 2000, 162:134-138