A glass passivation of a surface zener is not the same as a ion implant subsurface zener.
I only asked if the zeners weren't all subsurface.
"The resultant junction profile is determined by the background
concentration of the starting substrate, the amount of dopant
placed at the surface, and amount of time and temperature
used during the dopant drive-in. This junction profile
determines the electrical characteristics of the device.
During the drive-in cycle,
additional passivation oxide is
grown providing additional protection for the devices.
After junction formation, the wafers are then processed
through what is called a getter process. The getter step
utilizes high temperature and slight stress provided by a
highly doped phosphosilicate glass layer introduced into the
backside of the wafers. This causes any contaminants in the
area of the junction to diffuse away from the region. This
serves to improve the reverse leakage characteristic and the
stability of the device. Following the getter process, a second
photo resist step opens the contact area in which the anode
metallization is deposited."
The glass passivation is a different step.
And also you cannot compare the (long term) stability of the LTZ1000 with that of a LT1021
No, but you can compare it to the LT1034 which was being suggested as a low cost source of a buried zener diode ... if you just want a cheap'ish buried zener reference without resistor divider the LT1021-7 provides that.