Shadowing Practice: Why Memory Prices Are Crazy High - Learn English Speaking with Video

This is a graphics card for home gaming, the RTX 5090.

On its board, the first thing you see is the GPU in the middle.

Around the GPU is a ring of video memory chip.

When the GPU is working, its instructions, data, and temporary results are stored here.

And this is one compute node in NVIDIA's GP300 AI data center system.

The node has four GPUs.

But around them, we cannot see memory chips like the ones on the 5090.

So can AI server GPU work without video memory?

Of course not.

Look closely.

Next to the four GPUs are two rows of small squares.

These are the memory chips.

But unlike the memory on the gaming card, they are not placed on the board by themselves.

They are packaged together with the GPU.

And this special kind of memory is the star of today's video, HBM.

HBM uses 3D stacking to give it a high bandwidth and pack more parts into a small space.

It is now a key part of high -end AI graphics card.

It's also one of the main reasons normal memory prices have gone up recently

so how does hbm work

and how is it made in this video we are going

to learn all about hbm hi everyone i'm richard from htx

studio this video was originally made by right not a very

talented chinese content creator with his permission we translate it into

english for you guys we hope you enjoy it hbm stands for high bandwidth memory.

Bandwidth means how fast data can be moved.

So high bandwidth simply means that data can move very fast.

The memory chips and the GPU are connected by wires.

They use voltage signals to send data.

For example, let's say we want to send this data 0 1 0 1 0.

We can use high voltage for 1 and low voltage for 0.

So the voltage on the wire becomes low, high, low, high, low.

If want to send the data faster we can make each

voltage state last for last time we make this low high

low high low become this low high low high low in other words we erase the frequency

but frequency is not the only way to move data faster we can also add more wires

and send different parts of the data at the same time

this increases the bus width bandwidth equals frequency times spot width

so to get more bandwidth we can raise the frequency increase the bus width

or do both But raising the frequency of video memory causes many problems.

The voltage on the wire cannot go from low to high in no time.

It also cannot go from high to low in no time.

The change takes time.

We must wait for the voltage to fully rise or fall before the next cycle can start.

So frequency has a clear limit.

A higher frequency also causes more noise between nearby data lines.

That is why HBM uses a very wide bus to get more bandwidth.

A normal GDDR7 memory chip like the ones on the RTX 5090 has a bus width of 32 bits.

The 5090 can use up to 16 of these memory chips.

That gives it a total bus width of 512 bits, but one HDBM3 memory stack has a bus width of 1024 bits.

This B300 GPU has 8 HDBM3 stacks around it, so its total bus width is 8192 bits.

But how can HBM fit such a wide bus into such a small space?

As we just said, memory sends data to the GPU through wires.

More wires means a wider bus.

One bit of bus width needs one wire for data.

A normal GDDR7 memory chip has a bus width of 32 bits.

This means there are 32 data lines between the memory chip and the GPU.

But in real life, it needs many more lines.

It also needs lines for power, addresses, clock signals, and more.

So a GDDR7 chip can have 266 connection points.

And that is only for a bus width of 32 bits.

HBM has a bus width of 1024 bits.

So it needs 1024 lines just for data.

After we add the lines for power, addresses, and other jobs, one HBM3E stack has 3982 connection points.

So this is HBM's first problem.

How can it fit so many connections into such a small space?

First, let's see how normal GDDR memory is made.

The main memory circuits are made on a thin piece of silicon, but this silicon die is very easy to break.

The contact points on it are also very small, so it is hard to work with and use.

That is why we need a packaged substrate.

It is made from woven glass fiber and epoxy resin.

It is much stronger than the silicon die.

The finished die is turned upside down and placed face down on the substrate.

The contact points on the die connect straight to the substrate.

Inside the substrate are many layers of wires.

They move the signals to the back of the substrate, where larger solder balls are added.

The substrate protects the silicon die.

It also moves the tiny contact points on the die to the back of a much stronger package.

This makes the next step like soldering it onto a circuit board much easier.

To make this kind of substrate, glass fiber cloth is first soaked in epoxy resin.

It is pressed at high heat until it becomes a hard board.

Then a layer of copper foil is placed on both sides to make the circuit.

A light -sensitive film is put on top of the copper.

A mask with the circuit pattern is placed over it.

Then ultraviolet light shines on the board.

The parts of the film hit by the light change.

A developing liquid then washes away the parts that were not hit by light.

That leaves some of the copper open.

The board is then placed in an etching liquid.

The open copper is eaten away, while the copper under the film stays.

This is how the circuit lines are made.

A real packaged substrate usually has four to eight layers.

They are stacked together like pancakes.

Small holes are made with a laser to connect the circuits on different layers.

But this way of making circuits has a big limit.

The circuit lines cannot be packed very close together.

The surface of glass fiber is rough and not flat.

So when the copper foil and the light -sensitive film are pressed onto it, small air bubbles can get trapped inside.

If a circuit line is too thin, one small bubble can break it.

There is another problem.

100

This process uses a liquid chemical to eat away the copper.

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But the chemical does not only eat downward.

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It also eats into the sides.

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If a line is too thin, the sides can be eaten away until the line breaks.

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Because of these limits, a normal packaged substrate cannot hold very dense circuit lines.

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And there is one more problem.

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Normal video memory must be soldered onto a PCB.

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The PCB then connects the memory to the GPU.

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A PCB is made in almost the same way as the substrate

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so its circuit lines also cannot be packed very close together.

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But HBM needs almost 4 ,000 connections.

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A substrate made from glass fiber cannot do this.

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Its surface is just too rough.

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We need a new material.

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The material is silicon.

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Yes, the same silicon used to make chips.

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We start with one large piece of silicon.

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Its surface is polished until it is very smooth.

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Then photolithography and etching are used to make very small grooves on its surface.

119

Copper is put into those grooves to form circuit lines.

120

The HBM chips no longer need to sit on a normal substrate.

121

They can be soldered straight onto this large piece of silicon.

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The GPU is also soldered straight onto it.

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Now the HBM and the GPU can connect through this silicon.

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This large piece of silicon which connects the chips together is called a silicon interpulsor.

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A silicon interpulsor is like a chip with no transistors.

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Its surface is even flatter than a mirror.

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This lets chip makers use photolithography, etching, and thin film deposition to make very fine metal lines.

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On a glass fiber substrate, the lines are more than 10 micrometers wide.

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But on a silicon interpulsor, they can be less than 1 micrometer wide.

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They can even be only a few hundred nanometers wide.

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This means the silicon interpulsor can hold tens or even hundreds of times more circuit lines in the same space.

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With the silicon interpulsor, HBM can fit many more connections into a small area.

133

And that solves the speed problem.

134

But AI chips needs one more thing from video memory, more capacity.

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An HBM stack and a normal GDDR memory chip take up about the same amount of space on the board.

136

A GDDR7 chip like the one on RTX 5090 can usually hold 2GB.

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Even if we put 16 of them around the GPU, the total is only 32GB.

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That is enough for gaming, but it is still too little for AI.

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So how can we increase the capacity?

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The answer is stacking.

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We stack several bare memory dies on top of one another.

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They can all use the same silicon interpulsor at the bottom.

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This let us increase the capacity many times without using more space at the bottom.

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But stacking many chips is not easy.

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Putting more than 10 memory chips on top of one another may look simple.

146

But there is one big problem.

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How does the chip on top talk to the chip below it?

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Can we pull wires out from the sides of every chip and connect them to the bottom?

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No, every layer would need thousands of wires.

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There would not be enough space on the silicon interpulsor and every wire would have to be very thin.

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Even gold wire cannot hang in the air at such a small size.

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So engineers came up with another idea.

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They make holes in the silicon and fill them with copper.

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Every memory chip connects to these copper columns.

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The data can move down through the columns and reach the silicon interposer at the bottom.

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This is called a through silicon via, or TSV.

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But making these holes is not easy.

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Each hole is only about 5 to 10 micrometers wide a normal drill cannot make a hole this small.

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The industry uses a method called deep reactive ion etching.

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It is also called the Bosch process.

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This is a silicon wafer that already has transistor circuits on it.

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Now we need to make deep holes in it.

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First, we put photoresist on the surface of the wafer.

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Then a lithography machine shines the pattern of the holes onto the photoresist.

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The parts hit by the lights change.

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A developing liquid washes these parts away and opens the silicon below.

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Next, sulfur hexafluorid gas or SF6 enters the chamber.

168

A radio frequency coil turns the gas into plasma and makes three fluorine radicals.

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These fluorine radicals react with the open silicon.

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This makes silicon tetrafluorid gas.

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In simple words, the silicon is eaten away.

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But this does not only happen downward.

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It also happens sideways.

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If we keep doing this, we will get a large round space instead of a straight deep hole.

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So after FS6 has been used for a short time, it is stopped.

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Then Octafluorocyte cubitane or C4F8 enters the chamber.

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It is also turned into plasma.

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This makes fluorocarbon radicals.

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They gather on the silicon and form a protective film.

180

Then FS6 enters the chamber again.

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But this time, the protective film stops it from eating the silicon.

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When SF6 is turned into plasma, it makes both fluorine radicals and charged ions.

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An electric field guides these ions straight down towards the wafer.

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The ions hit the protective film at the bottom of the hole and remove it.

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Because the ions move straight down, they only remove the film at the bottom.

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The film on the sides stays in place.

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Now the etching glass can keep eating the silicon at the bottom.

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Then the same steps happen again.

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Ash, protect, pit.

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Ash, protect, pit the hole slowly gets deeper.

191

A silicon wafer may begin around 700 to 800 micrometers thick, but at this stage, the hole may only be etched about 100 micrometers deep.

192

Later, the wafer will be made thinner from the back until the hole comes out the other side, but we do not make it thinner yet.

193

First, we need to fill the hole with copper.

194

We use vapor deposition to put a layer of silicon dioxide on the inside wall of the hole.

195

This layer is very dense and does not carry electricity.

196

It It is like putting a tiny ceramic tube around the copper column.

197

It keeps the copper away from the silicon, but this is still not enough.

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Copper items can move around.

199

Over time, they can move into the silicon.

200

If this happens, they can damage the crystal structure of the silicon.

201

So we need another layer between the silicon dioxide and the copper.

202

This is called a barrier layer.

203

It is often made from tantalum or tantalum nitride.

204

The layer is only a few nanometers thick, but it can stop copper items from moving into the silicon.

205

Next, a very thin copper seed layer is put on top of the barrier layer.

206

Then a wafer is placed in the copper sulfate liquid for electroplating.

207

Copper ions slowly build up on the bottom and the walls of the hole.

208

In the end, copper fills the entire hole.

209

The wafer is then ground thinner from the back onto the hole and the copper inside are open.

210

Now we have a copper connection that goes through the silicon.

211

This is how one layer is made.

212

Next, lithography and electroplating are used to grow tiny copper bumps on top of the open copper columns.

213

Their tops are covered with a thin layer of tin.

214

These are called micro bumps.

215

Now we can stack several memory dies together.

216

We heat them and press them.

217

The tin on the micro bumps melts and solders the layers together.

218

Now every chip is connected through the copper columns and the micro bumps.

219

Data from the top layers can move all the way down to the silicon interposer.

220

At this point, the main memory part of HBM is finished, but the chip is still very easy to break, so we cannot use it yet.

221

As we said before, every memory die has been ground down to a thickness of only a few dozen micrometers.

222

The thin dies are held up by tiny micro bumps between them.

223

It is like a thin sheet of dry seaweed hanging in the air.

224

A small force can break it.

225

The answer is to fill the spaces between the dies, so they are no longer hanging in the air.

226

There are two main ways to do this.

227

Only three companies can mass -produce HBM today, SK Hynix, Samsung, and Micron.

228

SK Hynix uses the first method.

229

It stacks all the dyes first, then it heats the whole stack and solders all the micro bombs at the same time.

230

The full stack is put into a mold.

231

Liquid epoxy resin is poured into the spaces between the dyes, heat and pressure that make the resin hard.

232

Samsung and Micron uses another method.

233

They put a thin polymer film between every two dyes.

234

Under heat and pressure, the film melts and the micro -bombs are soldered together.

235

Then the film becomes hard as it cools.

236

They repeat this process one layer at a time.

237

The SK Hynix method works better in two ways.

238

First, it solders the whole stack at once instead of doing it one layer at a time, so it is much faster to make.

239

Second, there is nothing else between the chips when the micro -bombs are being soldered.

240

This means fewer things can go wrong, so the yield is higher.

241

HBM has many chips stacked on top of one another, so heat is a big problem.

242

To help heat move out, makers add extra through silicon vias.

243

These extra vias do not carry data, they are only used to move heat.

244

SK Hynix also mixes particles that carry heat well into the epoxy Ryzen.

245

This makes the epoxy work a little like thermal paste, so their HBM can move heat away about twice as well as Samsung's.

246

This has helped SK Hynix became the biggest company in the HBM market.

247

Their market share is about 50%.

248

With a silicon interposer, HBM can have a bus width of 1 ,024 bits.

249

And by stacking memory dice, HBM can hold a lot more data.

250

In this GP300 server node, every HBM stack has 12 memory layers.

251

Each stack can hold 36GB.

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Each GPU has 8 HBM stacks.

253

So that is 288GB for 1 GPU.

254

The node has 4 GPUs.

255

So it has 1 ,152GB of video memory in total.

256

That is more than 1TB in just one server node.

257

So how much does one node cost?

258

About $300 ,000.

259

Today, HBM3E is the version used at a large scale, but companies have already started making HBM4.

260

HBM4 has a buzz width of 2048 bits, so it can stack up to 16 memory layers.

261

So HBM4 needs even denser connections and an even taller stack.

262

HBM4 still uses micro bombs to join the layers, but it may be the last HBM generation to use them.

263

As the connections get denser, the space between the micro bombs gets smaller.

264

During soldering, two nearby micro bombs may join by mistake.

265

This can cause a short circuit, so in the future, HBM may remove the micro bombs.

266

Instead, two clean and smooth copper surfaces will be pressed straight together.

267

The copper items will move into each other and form one piece.

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This is called hybrid bounding without micro bumps the connections can

269

be packed closer together the stack can be shorter heat can move out more easily

270

and no epoxy is needed between the layers

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but we still do not know

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which hbm generation will use this technology at a large scale

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a few years ago the plan was to use it in hbm4

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but that did not happen and

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that is all for this video hbm has helped ai grow by giving it the key memory

276

and computing base it needs but hbm uses many of the same processes and machines as normal DRAM.

277

So making more HPM takes production space away from normal memory.

278

This means there's not enough normal memory for everyone who wants it.

279

So prices go up.

280

Do you believe in the future of HPM?

281

Do you believe in the future of AI?

282

That's it for this video.

283

See you next time.

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Vocabulary and speaking notes for this lesson

This C1 speaking lesson is built on the video “Why Memory Prices Are Crazy High”. The speaker keeps coming back to these words: silicon, memory, hbm, copper, chip. This video has 283 sentences and 3140 words to shadow. The speech runs for 16:58. The speaker talks fast, about 185 words per minute, so expect linked and reduced sounds. Only 76% of the words are among the 3,000 most common in English, so the vocabulary is demanding.

Key vocabulary in this video

The 15 most advanced words in the video, with pronunciation and meaning:

Word	Pronunciation	Meaning
silicon noun	/ˈsɪləˌkɑn/	A nonmetallic element (symbol Si) with an atomic number of 14 and atomic weight of 28.0855.
stack noun	/stæk/	A large pile of hay, grain, straw, or the like, larger at the bottom than the top, sometimes covered with thatch.
substrate noun	/ˈsʌbˌstɹeɪt/	An underlying layer; a substratum.
width noun	/ˈwɪtθ/	The state of being wide.
microwave noun	/ˈmaɪkɹoʊˌweɪv/	An electromagnetic wave with wavelength between that of infrared light and radio waves.
solder noun	/ˈsɒl.də(ɹ)/	Any of various easily melted alloys, commonly of tin and lead, that are used to mend, coat, or join metal objects, usually small.
wafer noun	/ˈweɪ̯fɚ/	A light, thin, flat biscuit/cookie.
bandwidth noun	/ˈbændwɪdθ/	The width, usually measured in hertz, of a frequency band.
voltage noun	/ˈvəʊltɪd͡ʒ/	The difference in electrostatic potential between two points in space, especially between live and neutral conductors or the earth.
epoxy adjective	/ɪˈpɑk.si/	Derived from an epoxide.
etch verb	/ɛt͡ʃ/	To cut into a surface with an acid or other corrosive substance in order to make a pattern. Best known as a technique for creating printing plates, but also…
micrometer noun	/maɪˈkɹɑmɪtəɹ/	A device used to measure distance very precisely but within a limited range, especially depth, thickness, and diameter.
node noun	/noʊd/	A knot, knob, protuberance or swelling.
bump noun	/bʌmp/	A light blow or jolting collision.
fiber noun	/ˈfaɪ.bɚ/	A single elongated piece of a given material, roughly round in cross-section, often twisted with other fibers to form thread.

Phrasal verbs you will hear

Word	Pronunciation	Meaning
eat away verb	/it‿əˈweɪ/	To physically corrode or erode (something) gradually.
close together adjective		Near each other in time or space.
go up verb		To move upwards.
move out verb		To leave one's present location; to leave somewhere for another place.
come out verb	/ˌkʌm ˈaʊt/	To be discovered; to be revealed.
come up with verb		To manage to produce, deliver, or present (something) by inventing, creating, thinking of, or obtaining it.
go through verb		To travel from one end of something to the other.
hold up verb		To wait or delay.

Grammar in this video

The structures the speaker uses most, with the exact words from the video:

Structure	In the video
“Used to” used to + verb — a past habit or state that is no longer true	used to make · used to move
Passive voice be + past participle — the focus is on what happens, not who does it	are stored · are not placed · are packaged
Present perfect have/has + past participle — a past action that still matters now	have gone · has been · has helped

Pronunciation to watch

The “th” sounds: width /ˈwɪtθ/, bandwidth /ˈbændwɪdθ/, lithography /lɪθˈɒɡɹəfi/, thickness /ˈθɪknəs/, cloth /klɒθ/
Long words — get the stress right: micrometer /maɪˈkɹɑmɪtəɹ/, lithography /lɪθˈɒɡɹəfi/, deposition /ˌdɛp.əˈzɪʃ.ən/, ultraviolet /ˌʌltɹəˈvaɪələt/

How to practise with this video

Listen to the whole video once without speaking and note the words you do not know.
Start at 0.75× speed, shadow it sentence by sentence, then go back to normal speed once it feels easy.
Record yourself and compare with the original, paying attention to words like silicon, stack, substrate.

What is the Shadowing Technique?

Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.

Shadowing technique: read the full step-by-step guide →

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