| Summary: | 碩士 === 國立交通大學 === 電子工程系所 === 96 === This thesis investigates the current mismatch and derives a physical model. First, we have discussed the back-gate bias control on subthreshold circuit mismatch. We have measured the MOSFETs operated in subthreshold region with different gate widths and lengths. These MOSFETs were characterized with back-gate reverse and forward biases. We have observed that the devices operating in subthreshold region exhibited larger mismatch than those in above-threshold region. The is due to the exponential dependence of current on gate and bulk voltages as well as process variations. In the case of back-gate reverse bias, we have found that current mismatch increases as the magnitude of back-gate reverse bias increases. On the other hand, with the supply of back-gate forward bias, the current mismatch decreases with increasing the back-gate forward bias. The improvement in match is due to the gated lateral bipolar action in low level injection. We have also statistically derived an analytical model that has successfully reproduced the mismatch data in weak inversion for different back-gate biases and different device dimensions. With this model, the current mismatch can be expressed as a function of the variations in process parameters. The extracted variations are shown to follow the inverse square root of the device area.
In the following work, we have used the results of extraction for different parameters. We also pay more attention to the threshold voltage fluctuation compared to different models. The substrate bias dependence of threshold voltage standard deviation was also discussed. On the other hand, we have found that drain voltage bias caused the effect of DIBL.
To reconfirm the reliability of our model, we have taken some parameters into account. In order to obtain the effective channel length, we have used the edge direct tunneling (EDT) model to gain the overlap length. On the other hand, the source/drain series resistance is also an important pole in our model. By incorporating the constant mobility criterion into the current equation under different bias conditions, the series resistance can be easily achieved.
In the beginning, we have discussed the devices operated in the subthreshold region. In the end, we have discussed the current mismatch in above-threshold regions and derived a physical model based on backscattering theory. Due to the backscattering theory, we have discussed the devices operated in saturation region. We have also derived a backscattering based mismatch model with key parameters, DIBL, threshold voltage, and backscattering coefficient. The effective channel length and series resistance were also taken into consideration to confirm the validity of the mismatch model. We have achieved that the backscattering coefficient mismatch model was feasible for our data. We have also successfully used the new mismatch model to reproduce the experimental current mismatch.
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