Yves Pétremand

Microfabricated rubidium vapour cell with a thick glass core for small-scale atomic clock applications

This paper presents a new fabrication method to manufacture alkali reference cells having dimensions larger than standard micromachined cells and smaller than glass-blown ones, for use in compact atomic devices such as vapour-cell atomic clocks or magnetometers. The technology is based on anodic bonding of silicon and relatively thick glass wafers and fills a gap in cell sizes and technologies available up to now: on one side, microfabrication technologies with typical dimensions <= 2 mm and on the other side, classical glass-blowing technologies for typical dimensions of about 6-10 mm or larger. The fabrication process is described for cells containing atomic Rb and spectroscopic measurements (optical absorption spectrum and double resonance) are reported. The analysis of the bonding strength of our cells was performed and shows that the first anodic bonding steps exhibit higher bonding strengths than the later ones. The spectroscopic results show a good quality of the cells. From the double-resonance signals, we predict a clock stability of approximate to 3 x 10(-11) at 1 s of integration time, which compares well to the performance of compact commercial Rb atomic clocks.

Microfabricated alkali vapor cell with anti-relaxation wall coating

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 indium-bonding 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 wall-coated cell are used to evaluate the cells 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.

Low-temperature indium-bonded alkali vapor cell for chip-scale atomic clocks

A low-temperature sealing technique for micro-fabricated alkali vapor cells for chip-scale atomic clock applications is developed and evaluated. A thin-film indium bonding technique was used for sealing the cells at temperatures of ≤140 °C. These sealing temperatures are much lower than those reported for other approaches, and make the technique highly interesting for future micro-fabricated cells, using anti-relaxation wall coatings. Optical and microwave spectroscopy performed on first indium-bonded cells without wall coatings are used to evaluate the cleanliness of the process as well as a potential leak rate of the cells. Both measurements confirm a stable pressure inside the cell and therefore an excellent hermeticity of the indium bonding. The double-resonance measurements performed over several months show an upper limit for the leak rate of 1.5 × 10−13 mbar·l/s. This is in agreement with additional leak-rate measurements using a membrane deflection method on indium-bonded test structures.

Low-temperature thin-film indium bonding for reliable wafer-level hermetic MEMS packaging

This paper reports on low-temperature and hermetic thin-film indium bonding for wafer-level encapsulation and packaging of delicate and temperature sensitive devices. This indium-bonding technology enables bonding of surface materials commonly used in MEMS technology. The temperature is kept below 140 degrees C for all process steps and no surface treatment is applied before and during bonding. This bonding technology allows hermetic sealing at 140 degrees C with a leak rate below 4 x 10(-12) mbar l s(-1) at room temperature. The tensile strength of the bonds up to 25 MPa goes along with a very high yield.

Low-temperature indium hermetic sealing of alkali vapor-cells for chip-scale atomic clocks

We present a low-temperature indium hermetic bonding technique on wafer level without using flux, active atmosphere or other pretreatment of the indium. Its simplicity and low temperatures allow encapsulation of sensitive MEMS devices. Bonding stronger than 18 MPa was accomplished with temperatures never exceeding 140°C. Leak rate measurements revealed leak rate below 2.5 × 10-12 atm cc/s. This bonding technique is then applied to fabricate rubidium vapor-cells for chip-scale atomic clocks (CSAC). Saturated absorption spectroscopy performed two and five months after fabrication confirms less than 1 mbar of gas contamination, and the retrieved clock signal demonstrates the suitability of the cell for clock applications.

Optimization of a chip-scale Rb plasma discharge light source: Effects of RF drive frequency and cell impedance

We report on the performance improvements achieved on our previously demonstrated proof-of-concept chip-scale dielectric barrier discharge (DBD) Rb lamp [1], (1) with change in the plasma regime of operation by changing RF drive frequency and (2) with an improved electrode design, for optical pumping in a chip-scale Double-Resonance (DR) atomic clock. Our realized microfabricated planar DBD Rb lamp now has externally deposited Al electrodes, allowing for efficient power coupling to the discharge volume and was tested at different RF drive frequencies ranging from 2 MHz to 500 MHz. Currently the light source can emit up to 380 µW of optical power on the Rb D2 line depending on input conditions.

Microfabrication and packaging of a Rubidium vapor cell as a plasma light source for MEMS atomic clocks

We report on the micro-fabrication and characterization of a chip-scale plasma light source based on a Rubidium (Rb) vapor cell. The Rb plasma light source is intended for use as an integrated optical pump-light source in miniature double-resonance Rb atomic clocks [1, 5]. The RF plasma is capacitively coupled using external electrodes, and the light source is impedance matched to the source for frequencies between 1 and 36 MHz. Rb vapor cells have been previously developed as reference cells for atomic clocks but not as light sources. This is the first reported Rb plasma emitted from a chip-scale device. Stable light emission is observed for over 18 days.

Laser-pumped double-resonance clock using a micro-fabricated cell

In view of a novel miniature atomic clock with low power consumption, we investigate on the potential for a laser-pumped double-resonance atomic clock based on a micro-fabricated Rb vapor cell. We obtain a clock short-term stability of 2×10⁻¹¹ τ^−1/2 and the stability stays below 1×10⁻¹¹ up to τ = 10⁴s, which demonstrates the feasibility of the approach.

Low-Power chip-scale Rubidium plasma light source for miniature atomic clocks

We present the development, testing and characterization of a low-power chip-scale Rubidium (Rb) plasma light source designed to serve for optical pumping in miniature atomic clocks. The technique used is electrodeless capacitively coupled plasma (CCP) discharge, driven in a micro-fabricated Rb vapor cell. The device is electrically driven at frequencies between 1 and 36 MHz to emit 140 µW of stable optical power while coupling < 6 mW of electrical power to the discharge cell. To our knowledge this is the first reported Rb plasma emitted from a chip-scale device.

NEMS based tools for nanoscience and atomic clocks

Nanoscience is a thriving multi-disciplinary activity, which aims at understanding the properties and the interaction of very small objects on the nanometer scale. In this endeavor, tools for the observation, analysis and modification of individual objects like macromolecules, clusters or even single atoms are required. The development of dedicated microfabricated instruments to measure physical and chemical interactions at this scale is therefore required. This talk will give an overview of microfabrication techniques employed to shape such NEMS based tools and introduce the audience to several probing techniques. In a second part, we focus on the principles and fabrication techniques of atomic clocks.