This is a commonly misunderstood misused set of terminologies.
First off these are not PIN Photodiodes - which stands for P - Intrinsic- N. These have large depletion regions for higher internal QE (Quantum Efficiency) and faster response. You can't make an array with this design though.
Pinning, refers to fermi-level pinning or pinning to a certain voltage level. Or also the forcing or prevention of the fermi-level/voltage from moving in energy space.
You can get surface state pinning from the dangling Si/SiO2 bonds providing trapping centers. A buried PD (Photodiode) has a shallow implant that forces the charge carriers away from these surface traps. The Si/SiO2 surface contributes to increased leakage (dark current) and noise (particularly 1/f noise from trapping/de-trapping). So confusingly a buried PD avoids pinning of the fermi-level at the surface.
A pinned PD is by necessity a buried PD, but not all buried PD's are pinned. The first Pinned PD was invented by Hagiwara at Sony and is used in ILT CCD PD's, these same PD's and the principles behind this complete transfer of charge are used in most CMOS imagers built today.
A pinned PD is designed to have the collection region deplete out when reset. AS the PD depletes it becomes disconnected from the readout circuit and if designed properly will drain all charge out of the collection region (accomplishing complete charge transfer). An interesting side effect is that the capacitance of the PD drops to effectively zero and therefore the KTC noise \$ q_n = sqrt(KTC) \$ also goes to zero. When you design the depletion of the PD to deplete at a certain voltage you are pinning that PD to that voltage. That is where the term comes from.
I've edited this Answer to acknowledge Hagiwara-san's contribution. It has long been incorrectly attributed to Teranishi and to Fossum (in CMOS image sensors)
OK a table of volumetric heat capacity for @gbulmer.
Material Heat capacity (J/(K*cm^3)) at 300K.
Aluminum 2.42
Copper 3.4
Iron 3.5
Al2O3 3.0
G-10 2.7
Nylon 1.7
Addition: Guesstimate of time constant for through hole resistor.
So let's just assume the whole thing is made from ceramic, say Alumina. Thermal conductivity is k = 30 W/(m* K) = 30mW/(mm* K) (millimeters will be easier for me) And make the diameter 2 mm (area = ~3mm^2) and the length 6mm. Then thermal conductivity (end to end) is
R = 1/k * l/Area = 67 K/W. Then the heat capacity is 3J* volume (cm^3) = 18 mJ/K. Now we need to scale the thermal resistance by some amount. I'll guess 1/2 (say 30K/W) but this is most likely not enough. (I'll over estimate the time constant.) Then the time constant is 30k/W*18mJ/K = 0.54 seconds. So that seems OK, but maybe high.
As an interesting aside I once tried to measure how much of the heat in a through hole resistor comes out through the leads. The answer was basically zero, except with very small heat input... and the numbers were still "in the noise". Through hole resistors are meant to cool by convection around the body.
Best Answer
CCD's are made from Si which has a bandgap of 1.12 eV. This means that it can sense a limited amount of thermal radiation at about ~ 1 um wavelength or shorter. This is called Near IR or NIR. Thermal sensors in the meantime, sense thermally emitted radiation ~ 10 - 14 um wavelength (this is the radiation emitted by a warm body at ~ 300 kelvin). The photons associated with a thermal IR scene are 10X as long and therefore 1/10 th the energy of a NIR photon (1 um vs. 10 um). For a direct bandgap detector, Like MCT (Mercury Cadmium Telluride) these must be cryogenically cooled (77 Kelvin) or the detector will get swamped by it's own heat. There are bolometer based sensors that are less sensitive. But a FLIR is specifically a MCT detector. MCT as a detecting material is very expensive with low yields.