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Solid-State Memory Cells

A transistor is a semiconductor switch that controls electron flow but cannot store data on its own. By adding a charge trap layer, engineers transformed the transistor into a memory cell capable of permanently holding a single bit of information.

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About this video

A transistor is a semiconductor switch that controls the movement of electrons through a circuit. When voltage is applied to the gate, the transistor either permits or blocks electron flow, representing a one or a zero. Different transistor types behave differently — some allow current when a one is applied, others when a zero is applied — but in all cases, the logic is defined by the input at the gate. The fundamental limitation of a basic transistor is that it has no mechanism to retain state. Once power is removed, any record of its previous condition disappears. In the 1960s, this limitation was overcome by introducing a charge trap into the transistor's structure, positioned between its semiconductor layers. The charge trap captures the electrical state set by the gate and holds it permanently, independent of whether power remains applied. This modification transforms the transistor into a memory cell — a device capable of storing a single bit of data. To retrieve that stored bit, power is applied to one side of the cell, and the output — a one or zero — reflects the state locked into the charge trap. This architecture forms the foundational principle behind persistent digital storage.

What you'll learn

Explain how a transistor functions as a switch and describe how the addition of a charge trap converts it into a memory cell capable of storing a single bit of data

What's covered

Transistors & Memory Cells

Transistor Basics
- Semiconductor Switch
  - Gate Controls Flow
  - Electrons Pass or Stop
- Represents 1 or 0
- No Data Storage
Types of Transistors
- Different Logic Behaviors
- 1 Stops or Allows Flow
- 0 Stops or Allows Flow
Memory Cell Creation
- Invented in 1960s
- Charge Trap Added
  - Sits Between Layers
  - Permanent State Change
- Stores One Bit
Reading & Writing Memory
- Apply 1 to Gate
  - State Saved in Trap
- Power Removed
  - State Still Exists
- Apply Power to Read
  - Outputs 1 or 0

Aligned to

CompTIA Tech+

1.3 Illustrate the basics of computing and processing.

2.5 Compare and contrast storage types.

Key terms

Transistor: A microscopic electronic switch found in microprocessors that represents a binary one (on) or zero (off) using electrical voltage.
Memory Cell: A storage unit created by adding a charge trap to a transistor, capable of permanently storing a single bit of data as either a one or zero.
Charge Trap: A layer added between the gate and semiconductor of a transistor that permanently retains an electrical state, enabling the transistor to store a bit of data even without power.
Bit: Short for binary digit, the smallest unit of data in computing, holding a single value of 0 or 1; all digital information is ultimately composed of bits.

Topics

Solid State Storage Transistors Charge Trap Memory Cells Computer Hardware Semiconductors

Transcript

This right here is a transistor. It's just a mini switch. It doesn't hold any information, however we figured out how to add something to this to turn it into a memory cell.

Inside a Transistor

Here's a diagram of a transistor. Right here we have a semiconductor material that can either pass electricity through it or not pass electricity through it, depending on what we put into the gate. We apply power to this, and if we were to put some voltage into it — we'll represent it as one — it may allow power through here. Or a zero, meaning the electricity is off, then it won't allow power to go through and it will stop the flow of electrons. Now that's not the only type of transistor there is out there, but that's just one example.

You can think of this as like a button right here. Imagine if I were to press this, it would complete the circuit, allowing the electrons to go through it. However, if this is not depressed, then electrons are not going to be able to pass through this circuit. So essentially this is a button, or once again a switch.

Making Switches Do Different Things

These transistors, or switches, we can create in different ways to do different things, and we call this some sort of logic to it. So what we do is we apply power to this side of it right here. Let's say we apply power — we're going to just represent power at the top here as one — maybe it allows flows of electrons, and so we get one out of this. Or perhaps what we do is we apply a zero to it, and then it will stop that flow of electrons.

There's also different types of transistors, so there are some transistors that if we apply one to it, it will stop the flow of electrons, or we can apply a zero to it to allow a flow of electrons. But essentially we can make these switches do different things depending on what we want to achieve out of it.

A Transistor Cannot Store Data

When it comes to these transistors themselves, there's really not a mechanism to store data in a transistor. That is, when we press this button it's either going to allow electrons to flow or not allow electrons to flow, depending on what kind of transistor it is. But essentially, as soon as we take away the power from this, the switch is no longer going to be operating. It's not going to really store any data in a transistor itself.

The Memory Cell

In the 1960s somebody took a transistor and created a memory cell from it. A memory cell stores a single bit of information. So what we have right here is we have added a charge trap in between the two layers here. We have a gate that we apply power to, and then that changes the state of this charge trap down here, and that charge trap is something that's permanent, that doesn't go away. So now we can either permanently allow the flow of electrons or stop the flow of electrons, based off the state of this charge trap. Now we have something that stores memory.

Here's a little different way to look at this. If we apply a one to the gate right here, that state gets saved in this charge trap, and now even if we take power away from it, that state still exists. Now if we want to figure out what bit this is, is it a one or zero, we just apply power to this side and we are going to get a one or zero.

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