I once made a single-transistor latch by accident. It acted as a single bit of memory and retained its value for weeks until I got bored with the project.
I had been making magnetic snap-together circuits, so I had a bunch of small PCBs with simple 2- and 3-pin footprints and holes that I soldered neodymium disc magnets into.
I put a big TO-220 N-fet on one of them, and stuck it to a laminated whiteboard so that the magnets stuck without shorting together, then I hooked it up to an LED as a simple high-side switch.
When I bent the transistor so that its metal plane rested against the magnetic whiteboard, its gate would latch after briefly tapping either V+ or ground to the magnet which was connected to the pin. When the transistor's metal plane was perpendicular to the board, it didn't latch. Disconnecting and reconnecting the LED didn't perturb the 'saved' value, and neither did removing power overnight. And the same thing happened with a similar P-fet connected as a low-side switch.
It probably wasn't a "real" latch; it was a very over-sized transistor with low gate capacitance, and I didn't try it with something like a 3904. I think it might have had something to do with the principles behind nonvolatile ferroelectric RAM, but I never did get to the bottom of it.
I think you just made a single bit of DRAM. It's surprising how long charges can stay around given suitably dry climate and insulators, and LEDs don't require a lot of power to light up either. A TO-220 package suggests a power transistor, so it will have substantially more gate capacitance than a typical logic-level one.
FWIW I'm told that decades ago latches were implemented as a tristate driver followed by an inverter or buffer. The source & drain cap, along with gate & wire cap, acted as the memory.
I had been making magnetic snap-together circuits, so I had a bunch of small PCBs with simple 2- and 3-pin footprints and holes that I soldered neodymium disc magnets into.
I put a big TO-220 N-fet on one of them, and stuck it to a laminated whiteboard so that the magnets stuck without shorting together, then I hooked it up to an LED as a simple high-side switch.
When I bent the transistor so that its metal plane rested against the magnetic whiteboard, its gate would latch after briefly tapping either V+ or ground to the magnet which was connected to the pin. When the transistor's metal plane was perpendicular to the board, it didn't latch. Disconnecting and reconnecting the LED didn't perturb the 'saved' value, and neither did removing power overnight. And the same thing happened with a similar P-fet connected as a low-side switch.
It probably wasn't a "real" latch; it was a very over-sized transistor with low gate capacitance, and I didn't try it with something like a 3904. I think it might have had something to do with the principles behind nonvolatile ferroelectric RAM, but I never did get to the bottom of it.
https://en.wikipedia.org/wiki/Ferroelectric_RAM