Electrons are stored in "trap" layers of Silicon between the gate of a transistor and the channel of the transistor. On either side of this trap layer is dielectric that blocks the electrons from leaving.

From my experience in a calibration lab for two different major electronics companies in the past few years, I can wholeheartedly say that Agilent products are generally the best of said brands. (Needing recalibration less often, better interfaces (IMO), less glitches in software, better build / support, etc.). That said, they are often the more expensive brand. At an academic research lab, this factor may take the most consideration depending on your funding sources and reliability. FWIW, we viewed most of the Tektronix equipment as junk and would opt to use the Agilent equipment when available (but, "junk" is a relative term).