Structural Analysis of

Updated: Aug 3

Microchips are advanced electronic devices, comprising a dense network of microscopic semiconductors, built-in layers on a thin wafer of semiconducting material usually silicon. These tiny circuits are normally hidden from view, but there are certain exceptions where we Miare allowed a peek inside at the surface layer of microchip silicon die. What attempt to do now...... we take you on a brief tour of the visible internal workings of a microchip and explain how they work.

View of Microchip under Optical Microscope

So, here's an example of a chip... And here's a far more sensible one. This one's EPROM, or EROM flavor, which stands for 'Erasable (Programmable) Read Only Memory' and these chips serve to provide an operational code or firmware to a system.

It's designed to be programmed once in the manufacture and can be erased only by shining an ultraviolet light onto the silicon through the quartz glass window. And window allows us to very easily see inside, and get a look at the surface layer of the silicon. So, when we look it under an optical microscope, at just 100x magnification, there isn't all that much detail visible, but we can see the majority of the main parts.

The two large seemingly blank areas are called the memory blocks and can contain billions of tiny transistors, which each store a bit of data. This particular chip is a 27C512 from ST Microelectronics which can store 512Kbits of data, so will contain at least 512,000 of these transistors, each serving to store either a 1 or a 0, by switching on or off respectively. Increasing magnification, a bit just be able to make out a regular pattern of the transistors, this is around 800x magnification. 

What is this Supporting Circuitry?

Around the memory blocks, we find the supporting circuitry. This is used to interface between the thousands of transistors in the memory blocks and the external circuitry away from the chip through only the 28 pins on this package. It would be highly impractical to have one pin dedicated to each transistor - that would require over half a million pins on the package which for obvious reasons can't be done, so this circuitry does something convoluted to connect all these transistors in such a way that they can all be accessed through these few pins.

Further to the extremities of the silicon, we find the output buffer amplifiers, which interface the high output impedance of the silicon circuitry and the low input impedance of the external circuitry. This prevents the external circuity from loading the silicon circuits and interfering with their operation.

This is somehow similar in concept to just a unity gain op-amp, operating as a voltage follower. Off to the sides here we can see the bonding wires connecting the silicon with the pins on the package - there are 30 of them, presumably, a couple is paired up for current-carrying capability.

It's incredible to think that we can do this really, this is only a small ROM device. This is nothing compared to modern microprocessors. And this is just the top layer that we can see there's more going on underneath that we can't. 

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