A method for operating an implantable medical device includes determining the difference of the absolute value of the voltage of a test QRS complex and the voltage of a baseline QRS template at a plurality of corresponding sample points and detecting ischemia if the sum of the differences at the plurality of sample points is greater than an ischemia detection threshold. The method comprises the following steps: generating a plasma from air as the process gas, which forms reactive nitrogen and oxygen species; oxidizing NO to form NO2 at temperatures below 400\xb0 C. Provided is a vertical transistor including a channel formation region formed using an oxide semiconductor which has a wider band gap than a silicon semiconductor and is an intrinsic semiconductor or a substantially intrinsic semiconductor with impurities that can serve as electron donors in the oxide semiconductor removed.