Thank you Zlymex and VintageNut for letting me play in these reindeer games
I've been working on a little temperature controlled test environment and put it to work this weekend running tests on one of the ones
I got, hunting for an inflection point in the temperature response. I ran it at various currents from 3mA to 18mA, changing the temperature of the chamber from 23C to 40C. Consistent with the findings of others in this thread, the TC did not change sign in this interval, with the smallest tempco being at 18mA. (I observed roughly 25ppm/C at 18mA. Even though the test wasn't set up to accurately measure TC, it still seemed like a pretty linear temperature response from 23 to 35C at that current.)
I don't know what the die temperatures were, since I haven't done a pulsed current test yet. (I need a different setup to take measurements fast enough.)
I just got some enameled nichrome wire, so I'm going to try to turn one of things into a little oven and see if I can find the temperature response curve from the datasheet. Then I can use the zener voltage at that zero point to stabilize it.