Microfabricated alkali vapor cell with anti-relaxation wall coating

Abstract

We present a microfabricated alkali vapor cell equipped with an anti-relaxation wall coating. The anti-relaxation coating used is octadecyltrichlorosilane and the cell was sealed by thin-film indiumbonding at a low temperature of 140 C. The cell body is made of silicon and Pyrex and features a double-chamber design. Depolarizing properties due to liquid Rb droplets are avoided by confining the Rb droplets to one chamber only. Optical and microwave spectroscopy performed on this wallcoated cell are used to evaluate the cell's relaxation properties and a potential gas contamination. Double-resonance signals obtained from the cell show an intrinsic linewidth that is significantly lower than the linewidth that would be expected in case the cell had no wall coating but only contained a buffer-gas contamination on the level measured by optical spectroscopy. Combined with further experimental evidence this proves the presence of a working anti-relaxation wall coating in the cell. Such cells are of interest for applications in miniature atomic clocks, magnetometers, and other quantum sensors.Microfabricated alkali vapor cells are widely studied and employed for miniature devices such as atomic magnetometers, 1 atomic clocks, 2,3 or other quantum sensors. 4 The required low relaxation rates of the atomic ground-state polarization are generally achieved by adding buffer gases to the cells, which results in decreased collision rates of the alkali atoms with the cell walls, longer ground-state polarization lifetime, and therefore improved stability in the case of an atomic clock. Alternatively, the lifetime of the polarization can be increased by depositing anti-relaxation coatings on the cell walls. [5][6][7] Macroscopic ($few cm) alkali vapor cells equipped with anti-relaxation wall coatings have shown to be effective for the development of atomic clocks 5,8 and magnetometers.9,10 Such coatings are also of interest for miniature atomic clocks 8,11,12 and several studies aimed at finding an optimal coating that is compatible with microfabrication, 11,13 in particular, in view of the elevated process temperatures.

Study of the operation temperature in the spin-exchange relaxation free magnetometer

“…In particular, the application of low-buffer-gas-pressure cells coated with paraffin or OTS would reduce the spin destruction rate and significantly improve the intrinsic sensitivity further. 34,35 …”

Chip-scale atomic devices

“…Microfabricated alkali vapor cells have therefore been recently developed that use a low-temperature solder on silicon 155 or low-temperature cofired ceramic 125 for sealing, rather than anodic bonding, as shown in Fig. 20.…”

“…In Ref. 155, thermocompression bonding at 140 C was used to seal a cell, the interior of which was coated with octadecyltrichlorosilane (OTS), which is stable up to 170 C in the presence of alkali vapor. 156 This cell showed a hyperfine resonance linewidth of under 10 kHz, suggesting that the wall coating was acting effectively to prevent depolarization.…”

Non-negligible collisions of alkali atoms with background gas in buffer-gas-free cells coated with paraffin

“…However, background gas pressures in buffer-gasfree cells have not been reported except for a very high pressure (≤ 600 Pa) background gas in a microfabricated cell with an octadecyltrichlorosilane coating [15].…”