What well-known ICs have essentially no packaging?

Question

As a kid I once found a calculator whose IC was protected only by a loose plastic cover. With the cover removed, and with appropriate lighting, I could make out distinct features of the IC– including company logos– with a simple classroom microscope.

I'm just a lazy enthusiast; I realize that most ICs are more expertly packaged, and I have no interest in milling, dissolving, or chipping away at anything. How uncommon was my childhood discovery anyhow? Are there any well-known integrated circuits I could buy or find that I can gaze at without much hassle?

(In case anyone cares, the calculator I found was a CVS-branded "scientific calculator", model 185371.)

Answer 1

You can actually buy unpackaged ICs. They are sold as "bare die". Basically this means that the silicon has not been wire bonded into a package nor covered up.

I've come across a few things including a few TI ICs that are available as bare dies. In fact there is a whole page on the TI Website which lists parts they sell in this format. Other manufactures (e.g. NXP, Microchip, etc.) will also likely sell bare die versions of some of their ICs.

However, I'm not entirely sure whether any of these will be available in small quantities. Typically bare die stuff will only be used in very niche markets by people with the equipment to wire bond them. It is likely that you would have to need 1k+ units before the companies would be willing to sell them to you. In fact the reason most ICs are available in small quantities (other than samples) is that the big distributors buy in bulk and then resell to low volume customers.

A more economical option if you are just interested in looking at them (which is not surprising, they can be quite spectacular!), is to look on a well know auction site for "Silicon Wafer". There are quite a large number of processed (but electrically defunct) 6", 8" and larger wafers for reasonable prices (sub $30). These are even more spectacular than just a single die.

Answer 2

UVPROMs (Ultra-violet erasable read-only memorys) had a quartz window through which you could see the actual silicon chip.

Answer 3

A lot of the old (70's and 80's) uP, RAM and such were produced in ceramic packages for hi-rel or hi-temp use. These ceramic packages are easy to distinguish, since the ceramic is usually white or grey, not black. The chip is installed in a well in the middle of the package, and a piece of metal foil soldered around the edges covers it. If you clamp the IC down, it is usually possible to peel the foil away using an exacto knife or something similar.

In general, you're best off looking at old chips. The newest (as in the last decade or better) are made with such fine features, like 14 nm nowadays, that details are simply invisible in visible light.

eBay is probably a good place to start looking.

Answer 4

You might be looking for UV erasable microcontrollers. They were available from Intel, Microchip and others. They have a more complex and interesting structure (not just a memory array). Here is an Intel 8751H from this site:

There are plenty of die photos about, so you can compare. Here is one (AMD, not Intel) from Wikipedia.

The quartz window distorts the image a bit, but you can easily remove the one shown (try a propane torch) if you don't mind destroying the chip. They're not especially rare. Also, with 10um or whatever features, you can easily make out the structure with an optical microscope. The latest chips have features in the 20nm range (~500x finer), which is 1/20 a wavelength of visible light- that means ~250,000x more minimum size devices can fit in the same area.