Boosting Transistor Counts Without Smaller Nodes
As making ever smaller process nodes becomes more expensive and complex, chip engineers are searching for new ways to keep packing more transistors into CPUs and GPUs. A recent research project from MIT, the University of Waterloo, and Samsung Electronics takes a very different approach. Instead of shrinking everything further, they are adding a new layer of microscopic switches to the back of an already finished chip.
This idea is closely related to chip stacking, which you might have seen in modern 3D NAND flash or stacked cache designs. But here the focus is on adding extra transistor and memory layers directly into the back end of the chip. If this technique matures, it could mean huge gains in transistor density and more powerful processors for gaming PCs and high performance computing, without needing the next ultra tiny process node.
To understand why this matters, it helps to briefly look at how a modern chip is built. Traditional CMOS chips are made by repeatedly applying and etching layers of materials on top of an ultra pure silicon wafer. The bottom region, often called the front end, is where the actual transistors live. These are the tiny switches that do all the logic and data processing.
Above that sits the back end, a complex jungle of metal and insulating layers that carry power and signals around the chip. The back end is how electricity and data get to all those front end transistors so they can work together as a functioning CPU or GPU.
Putting Transistors Where Only Wires Used To Live
In theory, you could put multiple layers of transistors one on top of another to increase density. The problem is heat. The materials and processes used for traditional transistors require high temperatures, and if you try to build a second layer after the first is finished, you risk destroying the original layer underneath.
The MIT led team flipped the usual approach. Instead of trying to place a second transistor layer directly above the front end using the same hot processes, they built new transistors into the back end where only wires and insulators normally exist.
The key was finding materials that could be processed at much lower temperatures. The researchers used a very thin layer just 2 nanometers thick of amorphous indium oxide to create additional transistors in the back end. Because this material can be deposited at lower temperatures than standard transistor materials, it does not cook the delicate front end circuitry that is already in place.
They also experimented with using ferroelectric hafnium zirconium oxide in that same back end region. This material can act as the basis for memory cells, meaning that not only can you add more logic like extra switches, you can also potentially integrate new kinds of on chip memory in that space.
The result is a prototype structure where the back end is doing much more than routing power and signals. It is now host to additional active devices that increase the total transistor count without shrinking the process node.
Why This Matters For Future CPUs, GPUs, and Gaming
For gamers and PC enthusiasts, more transistors usually means more performance or more features. Higher transistor counts enable:
- More CPU cores and threads for better multitasking and modern game engines
- Larger and smarter GPU shader arrays for higher frame rates and better ray tracing
- Bigger caches and more on chip memory for reduced latency and smoother performance
- More dedicated hardware blocks for AI upscaling, encoding, and physics simulation
Traditionally, Moore’s Law delivered this by shrinking process nodes, going from, for example, 14 nanometers to 10 nanometers to 7 nanometers and beyond. However, each new step has become dramatically more expensive and technically challenging. At some point, just shrinking transistors gets harder, slower, and less cost effective.
This is why research like this matters. If engineers can layer transistors in the back end, then combine that with other techniques such as vertical transistor stacking and advanced 3D chip stacking, the limit on transistor density can be pushed far beyond what simple node shrinks allow.
Imagine a future gaming CPU or GPU that uses a combination of:
- Traditional front end logic on a cutting edge process
- Extra back end transistors adding specialized logic or memory layers
- Stacked cache dies or extra compute chiplets on top using 3D packaging
All of these methods together could massively increase the number of functional units and cache capacity without needing an impossibly tiny base node. That could translate into faster frame times, higher resolutions with demanding effects like ray tracing, and better AI assisted features such as DLSS style upscaling or advanced physics.
There is an important catch. The current work is research stage. The team has shown that they can build these back end transistor and memory structures and that they can coexist with the front end without destroying it. But turning that into full commercial CPUs and GPUs with complex architectures and billions of devices will take many more years of development and refinement.
Still, the direction is encouraging. Moore’s Law might look shaky if you only look at traditional node shrinks, but when you factor in new architectures, 3D stacking, and now back end transistor layers, there is plenty of room left to increase density and performance. For PC hardware enthusiasts and gamers, that means there are many more generations of more powerful chips ahead.
The next time you see headlines about Moore’s Law being dead, remember work like this. Engineers are not just fighting for smaller transistors. They are reinventing how and where transistors can live inside a chip. The future of CPUs and GPUs may not only be about going smaller but also about building upward and using every layer of silicon to its full potential.
Original article and image: https://www.pcgamer.com/hardware/mit-electronics-researchers-develop-a-new-way-to-fabricate-transistors-on-the-backend-of-finished-dies-to-keep-pushing-the-limit-of-chip-densities-ever-higher/
