Does a Flash Drive Weigh More Full?

Hypothesis before research:

Yes, as current is introduced into the flash drive the electrons from the external power source are stored in various configurations such that the total mass of the flash drive is increased, even if only by m_e (mass of an electron) times the number of electrons required to store final state.

Deep Dive

How is digital information stored at a high level?

Let’s start by breaking down how information is stored inside a flash drive at various depths of hardware technicality, down to the physical processes. At a high level most probably understand information in computing is stored in bits that are flipped between 0 and 1. Flash memory does this through something called NAND memory chips. NAND, if you’re familiar with logic gates, is a NOT-AND gate. NAND memory is composed of multiple transistors, usually metal-oxide-semiconductor field-effect transistors or MOSTFETs. Given a NAND gate, output is low when both of its inputs are high, otherwise the output is high. Inputs are given to the NAND gate with voltages applied to the gate terminals of the input transistors.

How can a NAND gate hold information?

For our simplified flash drive we’re going to assume they’re simply Floating Gate Transistors made of a combination of NMOS (N-channel metal-oxide semiconductors) and PMOS (p-channel metal–oxide–semiconductor) MOSFET transistors. When a charge is “stored” on the floating gate, it affects the threshold voltage of the transistor allowing it to maintain a binary state. None of this is particularly interesting, noteworthy, or even necessarily correct for all types of flash memory, but we’re not trying to answer the question of most common types of transistors and gate types used to store memory because under the hood they usually use the same physical properties to “hold” the value, so let’s take a look at how that physical process occurs.

What are the constituent parts of a PMOS transistor?

PMOS transistors are made of

substrate material
gate material
gate insulator
source and drain contacts
interlayer dielectrics for insulating
metal interconnects for interfacing with the rest of the circuit

Of these, the important ones for our question are the substrate and gate. The gate material is usually made of a polycrystalline silicon as it can be easily doped to be n-type or p-type depending on the transistor type (we’re not going to discuss doping types here). In p-type polysilicon conductors there are empty electron orbits in the valence band. These orbits are created by the introduction of acceptor dopant atoms, like boron, which contain fewer valence electrons than the host silicon. These empty orbits allow electrons to move between the atoms easily. Now we’re getting somewhere. We know memory uses induced voltage differences to trigger certain states in the circuit to cause current to pass through various gates and store the value, but how does that part work?

Where do the electrons come from?

When the voltage is applied to the gate of a PMOS transistor, the p-type polysilicon gains a positive charge storing a 0, corresponding to the higher voltage attracting electrons to the polysilicon gate. Likewise, to store a 0, you drop the voltage lower to displace the region’s electrons. When proper voltage is applied an inversion layer forms in the substrate material. This inversion layer is made of mobile electrons that move into the polysilicon creating a conductive path between the source and drain. Electron movement between these two materials, through a quantum process called Fowler-Nordheim tunneling, decides the final stored state of the transistor. This makes sense as you can power off a flash drive and maintain the circuit state. They wouldn’t be very useful without it.

TL;DR: Answer

No, a flash drive does not contain more mass, as the entire mass required to store values already exists inside the flash drive. The state of the drive’s electron configuration is simply shuffled to exist in various positions after induced voltages cause electrons to accumulate on the gate material or recede back to the substrate.