Wafer-level integration of micro heater on an alkali vapor cell for chip-scale SERF magnetometers is presented. In order to obtain a suitable resistivity, polysilicon and aluminum are mixed as the target material. Magnetron sputtering is adopted to fabricate the heater on the surface of the alkali vapor cell. Various voltages are applied to the heater, of which the temperatures are measured by thermal sensitive sensors. Spin exchange relaxation free (SERF) atomic magnetometer with the heater integrated on the alkali vapor cell is characterized. Results show that the micro heater is successfully integrated on the alkali vapor cell. With the integrated heater, the rubidium vapor cell is heated up to 120°C by a 445kHz AC current. The sensitivity of the SERF magnetometer is 6.3pT/Hz1/2. Results also indicate that it provides an effective and low-cost solution for the miniaturization of atomic magnetometers.
Wafer-level integration of micro heater on an alkali vapor cell for chip-scale SERF magnetometers is presented. In order to obtain a suitable resistivity, polysilicon and aluminum are mixed as the target material. Magnetron sputtering is adopted to fabricate the heater on the surface of the alkali vapor cell. Various voltages are applied to the heater, of which the temperatures are measured by thermal sensitive sensors. Spin exchange relaxation free (SERF) atomic magnetometer with the heater integrated on the alkali vapor cell is characterized. Results show that the micro heater is successfully integrated on the alkali vapor cell. With the integrated heater, the rubidium vapor cell is heated up to 120°C by a 445kHz AC current. The sensitivity of the SERF magnetometer is 6.3pT/Hz1/2. Results also indicate that it provides an effective and low-cost solution for the miniaturization of atomic magnetometers.
The designs of microfabricated alkali vapor cells play an important role when the atomic magnetometers are developing toward on-chip integration. This paper presents microfabricated spherical alkali vapor cells with improved sensitivity for chip-scale atomic magnetometers. A microfabricated spherical rubidium vapor cell and a traditional microfabricated planar rubidium vapor cell are designed for comparison, which are of the same volume and interconnected by a microchannel to acquire equal inner buffer gas pressure. In chip-scale spin-exchange relaxation-free (SERF) atomic magnetometers, the rubidium polarization lifetimes of three pairs of spherical and planar vapor cells at different buffer gas pressures of 0.35, 0.73, and 2.00 amg are measured, respectively. The sensitivity of SERF atomic magnetometers using the vapor cells at a 0.35-amg buffer gas pressure is also measured. The results show that the transverse polarization lifetime of the spherical vapor cell is 2.46, 1.44, and 1.05 times that of the planar one at 0.35-, 0.73-, and 2.00-amg buffer gas pressures, respectively. Combining the improved polarization lifetime and increased optical path length, chip-scale SERF atomic magnetometer using the microspherical vapor cell has the sensitivity of 60 fT/Hz1/2from 5 to 15 Hz, while that based on the planar one is demonstrated with the sensitivity of 400 fT/Hz1/2from 5 to 15 Hz.
Compared with superconducting quantum interference devices, chip-scale atomic magnetometers using the wafer-level micro alkali vapor cells can be used more conveniently in the applications of geophysical mapping, health care and remote monitoring. Drastic wall collisions and decreased polarization lifetime are the main barriers for the performance of the chip-scale atomic magnetometers. In this study, OTS organic films coated on the inner surface of the micro vapor cells were used to suppress wall collisions and improve polarization lifetime of the alkali atoms in the micro cells. First of all, the fabrication process of wafer-level micro OTS coated vapor cells is introduced, the process is based on anodic bonding technology. Then the prepared wafer-level micro OTS coated vapor cells have been characterized by the water-contact angle test and measured in the micro-machined spin-exchange relaxation free(SERF) atomic magnetometers. Results show that the OTS coating is effective after anodic bonding from the water contact angle test. Results also indicate that the spin exchange relaxation free atomic magnetometer using the micro OTS-coated vapor cell can operate successfully.
High sensitive SERF(spin-exchange-relaxation-free) atomic magnetometers play an important role in many fields including geophysical mapping, space science, nuclear magnetic resonance, health care and perimeter and remote monitoring. This paper presents a novel approach for the system integration of a SERF atomic magnetometer. First of all, Rb vapor cell integrated with micro heater and Helmholtz coils was selected as physic part of the system and the vapor cell was characterized by pressure broadening effect to analyze nitrogen buffer gas pressure in the vapor cell. Then optical module including laser, micro-lens to collimate light beam emitting from the laser, quarter-wave plate to circularly polarize laser beam was taken as optical pumping and probing source simultaneously, and the interaction of circularly polarized laser beam with rubidium atoms was detected by silicon PIN photo-detectors. At last, Laser module, physics part of the system and silicon PIN photo-detector were integrated on a glass wafer substrate benefiting from the characteristics of non-magnetic material and good flatness, based on the integrated SERF atomic magnetometer, weak magnetic field could be measured. Results demonstrate that the SERF atomic magnetometer is integrated successfully and could be used for the detection of weak magnetic field.
Spin-exchange-relaxation-free (SERF) optical atomic magnetometers are facing the challenges of dramatic decrease of sensitivity when the alkali vapor cells become small. This paper focuses on the sensitivity improvement of the chip-scale atomic magnetometer (CSAM) by changing buffer-gas pressures inside the microfabricated vapor cells. The rubidium vapor cells with three different buffer-gas pressures were tested in the SERF magnetometer. The influences of vapor cell temperature and pumping laser power on the device sensitivity are also characterized for further optimization. Results show that the three atomic vapor cells, with N2buffer-gas pressure of 0.20, 0.88, and 2.35 amg, have sensitivities of 900, 500, and 150 fT/Hz1/2, respectively. Results indicated that when the alkali vapor cells continue to be smaller, high buffer-gas pressure would provide an effective way to reduce the wall collision and improve the performance of CSAMs.
The spin-exchange relaxation-free (SERF) atomic magnetometer is one of the ultra-sensitive magnetometers, which must be operated in a low magnetic field and heated more than 100°C. One of the main engineering difficulties in fabricating a SERF atomic magnetometer is to develop a heater that introduces no additional magnetic noise into the measurement system. In this paper, a novel compact current-heating scheme and apparatus for the SERF atomic magnetometer are proposed. The thermal and magnetic simulations of this apparatus are carried out and the results of the simulations demonstrate the feasibility of this heating apparatus: the vapor cell can be heated to a temperature of 103°C and magnetic field introduced in the magnetometer can be limited in 10nT.
This paper introduces measurement of weak magnetic field using a novel design of chip-scale Spin Exchange Relaxation Free (SERF) atomic magnetometer based on a microfabricated Rubidium (Rb) vapor cell. The sensor, which integrates a micro-fabricated Rb vapor cell, a heater and related components, is fabricated by stacking printed circuit boards (PCB) and Micro Electro Mechanical Systems (MEMS) process technology. During the experiments, the noise of the measurement using the atomic magnetometer was obtained. In addition, a test of the simulated magnetic field was performed in a shielding cylinder, and the signal of the simulated magnetic field about 100 pT at 1.2 Hz was measured. The signal is processed by the software using a notch filter to suppress the Direct Current (DC) noise and 50Hz noise. This paper provides a novel micro-fabricated device for detecting weak magnetic field.