Most integrated circuits do not have a single failure temperature. They have a set of parameters that drift at different rates, and a point at which the drift stops being something the design can absorb. Knowing which parameter gives out first is what tells you whether a part can be pushed, redesigned, or replaced.
Leakage is the one that surprises people
Reverse-biased junction leakage scales with the intrinsic carrier concentration of silicon, which climbs exponentially with temperature. As a working rule, junction leakage roughly doubles for every 8 to 10 °C. That sounds manageable until you compound it: from 25 °C to 175 °C is fifteen or more doublings, a factor of tens of thousands.
Subthreshold conduction moves in the same direction. The subthreshold slope is proportional to kT/q, so a transistor that needs about 60 mV per decade of current at room temperature needs closer to 95 mV per decade at 200 °C. A device that was comfortably off is now leaking measurably.
For digital logic this shows up as standby current. For analog it is worse, because leakage lands directly on the nodes that hold information: sample-and-hold capacitors, integrator nodes, current mirrors, high-impedance sensor front ends. A picoamp of leakage across a 10 pF hold capacitor moves the stored voltage by 100 mV in a millisecond. At room temperature that same junction leaked femtoamps and nobody thought about it.
Threshold voltage and mobility move in opposite directions
Threshold voltage falls with temperature, typically somewhere between 0.5 and 2 mV/°C depending on process and doping. Across a 175 °C span that is a shift of roughly 100 to 350 mV. In a 3.3 V design that is a nuisance. In a 1.8 V design it is a redesign.
Carrier mobility falls at the same time, which reduces drive current. The two effects partly cancel, and there is a bias point — the zero temperature coefficient point — where drain current is nearly independent of temperature. Designing critical bias branches around that point is one of the oldest tricks in high-temperature analog, and it still works. It is also the reason a high-temperature design is not simply a normal design with a wider spec: the bias architecture has to be chosen for it from the start.
Latch-up margin shrinks exactly when you need it most
Bulk CMOS contains a parasitic thyristor formed by the well and substrate junctions. Two things happen as temperature rises: the current gain of the parasitic bipolar devices increases, and the well and substrate sheet resistances increase. Both reduce the holding current and the trigger current for latch-up.
So a layout that passed latch-up qualification at 125 °C has less margin at 175 °C, in a system that may also see more injected current from long cable runs and inductive loads. This is one of the clearest arguments for silicon-on-insulator at high temperature, and we look at that trade in a separate piece.
Interconnect wears out faster than the transistors
Electromigration failure follows Black’s equation: mean time to failure scales inversely with roughly the square of current density and exponentially with activation energy over kT. With an activation energy around 0.7 to 0.9 eV for aluminium interconnect, moving from 110 °C to 175 °C shortens interconnect lifetime by roughly an order of magnitude at the same current density.
The practical consequence is that the current density rules in the design kit have to be re-derived for the target temperature and target lifetime. A layout signed off against default rules is not signed off for 200 °C, even if every transistor still meets specification.
Time-dependent dielectric breakdown and bias temperature instability accelerate on similar Arrhenius terms. None of these are catastrophic on day one. They shorten the part’s service life, which is precisely the parameter that matters in a tool that is expensive to retrieve.
Non-volatile memory is often the first hard limit
Floating-gate Flash stores charge behind an oxide barrier, and charge loss is thermally activated. A cell qualified for ten-year retention at 85 °C can lose its margin in a very different timescale at 175 or 200 °C — the Arrhenius relationship is unforgiving, and it applies to data that was written cold and then baked.
This is why high-temperature microcontrollers so often use a different memory strategy: masked ROM, antifuse one-time-programmable arrays, or ferroelectric and magnetoresistive memories that do not rely on stored charge. It is also why “can I reprogram this in the field” is a question worth asking early, not after the architecture is fixed.
The package fails on a different schedule
Silicon is not the whole part. Gold wire on aluminium bond pads forms intermetallic phases whose growth is thermally accelerated, and Kirkendall voiding at that interface is a classic high-temperature wear-out mechanism. Die attach materials soften or degrade. Plastic moulding compounds pass their glass transition and change modulus, which changes the stress on the die. Coefficient of thermal expansion mismatch drives fatigue in solder joints under thermal cycling, following Coffin-Manson behaviour.
A die that holds specification at 200 °C in a ceramic package with an appropriate metallisation system is a different product from the same die in a standard plastic package, even though the datasheet numbers for the circuit are identical.
What this means when you are choosing parts
Three practical conclusions.
The maximum rating on a datasheet is not a performance guarantee. It usually means the part will not be destroyed. Whether the accuracy, offset, drift and timing specifications still hold at that temperature is a separate question, and is often answered only by a “typical” figure with no guaranteed limit.
Ask what was measured and what was extrapolated. Characterisation across the full envelope costs money and time. A supplier who has done it can show you the distribution. A supplier who has not will show you a simulation.
Decide the envelope before the architecture. Almost every mitigation in this article — the bias point, the process choice, the memory strategy, the current density budget, the package — is an architectural decision. Adding them late is expensive; choosing them first is nearly free.
If you are working on a system where the electronics have to sit at the process temperature rather than away from it, tell us the envelope and the lifetime. We will tell you what is achievable and what is not.