A flexible display device and a method for accurately recognizing a user’s flex input bending of the flexible display device is described. This device allows characterizing the ventricular repolarization wave of an ECG signal collected from a patient. A plurality of slits are included in the downstream surface, and each slit connects to at least two passages. A method for making the voltage non-linear resistor and a varistor using the same are also provided. An airflow generated by the fan has a portion flowing through the channels of the fins and another portion flowing between the body and the heat spreader for blowing a second heat generating electronic device by guiding of the sidewall of the guiding fin.