# What prevents semiconductors working below -40°C or so?

Most devices seem to be characterised over -40°C to ≥85°C. What limits them to cold temperatures? Can an IC be damaged by keeping it too cold? Does this apply to other devices, e.g. diodes, transistors?

• My guess is that the testing lab doesn't want to buy a -50C refrigerator. AMD Phenom II overclocking at -170C: youtube.com/watch?v=0Ggt9pA8X_c – joeforker Nov 19 '10 at 21:24
• @joeforker: Where does the "-170 °C" figure come from? There's bound to be a tremendous difference between "ambient" (liquid nitrogen) and the actual junction temperature when the processor is dissipating a few hundred watts of power. – Nick T Nov 19 '10 at 21:31
• It comes from the description on the Youtube video of course, only exceeded by the comments as an accurate and insightful source of information. – joeforker Nov 19 '10 at 22:08

Damage to an IC package at low temperatures while unpowered would be due to mechanical effects; differences in thermal expansion coefficients between the epoxy, lead-frame, and die.

Problems with operation would be due to increased resistance (semiconductors' temperature coefficient of resistance is negative). When the temperature and doping concentration is low enough, semiconductors will essentially become insulators and not conduct at all, causing unspecified operation.

Some ICs will operate just fine at cryogenic temperatures but they must start up warm to allow bandgap voltage references to boot.

In theory if some transistor "fails" due to carrier freezeout, the IC could damage itself elsewhere (not very likely, as most failure modes are thermal, and everything on the die is very tightly coupled.)

See the tutorial pages here for more.

### Edit:

As you note, most devices are characterized between usually -40 °C to +85 °C. Nothing says they will not work down to cryogenic temperatures.

• I always forget to note that to people. I just meant it stopped working, but It could damage it. – Kortuk Nov 19 '10 at 21:50
• +1 just for the link. I may be designing boards to go in a liquid argon environment (just a wee bit colder than liquid nitrogen) very soon, so I'm going to need practical advice... – dmckee --- ex-moderator kitten Nov 20 '10 at 1:19
• @dmckee You got me curious now :P, what sort of application are you using liquid argon for? I'd imagine liquid nitrogen would be much cheaper (and slightly colder? N2 b.p. 77 K, Ar b.p. 87 K) – Nick T Nov 20 '10 at 18:08
• A particle physics detector called a time projection chamber. Traditionally they've been gas phase, but it will work with the right liquids. Put a strong field across the fluid, and the charge tracks left by ionizing radiation will drift (many cm and at a reliable rate) to the field (and induction) wires where it can be detected and used to reconstruct the 3D geometry of the event. Argoneut has pictures from a test stand device. And I could have sworn the boiling point was 74 K. Ah well... – dmckee --- ex-moderator kitten Nov 20 '10 at 19:31

You can characterize parts yourself below -40, and mechanical failures can be largely avoided if the temperature cycle is slow.

Some package options work, some don't. heheh. you have to do that experiment yourself.

You can characterize parts below 0C yourself ( easily using a domestic freezer.)

Astronomers just love dunking stuff in liquid nitrogen to get rid of thermal noise in their camera chips and A/D converters.

For extreme conditions, fit heaters to significant parts (large caps, problem IC's.)

Then your power sequencing systems turns the heaters on till the parts are in a temperature range you've characterized.

Other than the physical aspects of cold silicon, -40/85C tends to fit the most stringent conditions that most folks would need (commercial/industrial).

Practically, characterizing a device is a very time consuming process because it requires test fixtures and other equipment capable of the temperature range. It's not about buying a better freezer since many devices are characterized using the same test equipment used for production testing. The fun part is collecting and parsing the characterization data just to realize that the test fixture froze over and started collecting garbage data.

• Just because the freezer is the same doesn't mean there is no extra cost to the test. Every degree lower you want to test costs time, which means money. – Warren Young Dec 28 '14 at 11:03