| AVS 60th International Symposium and Exhibition | |
| MEMS and NEMS | Monday Sessions |
| Session MN+AS+SS-MoM |
| Session: | Fabrication and Multi-scale Interactions of Materials, Surfaces, and Interfaces at the Micro- and Nano-scale |
| Presenter: | M. Serry, The American University in Cairo, Egypt |
| Authors: | M. Serry, The American University in Cairo, Egypt A. Sharaf, The American University in Cairo, Egypt |
| Correspondent: | Click to Email |
This paper reports on a new MEMS-based technique for the rapid and highly sensitive detection of gamma irradiation. The proposed sensor detects small doses of gamma photons through changes in the mechanical and electrical properties of the MEMS structure, which consists of a voltage controlled variable capacitor coated with a gamma photons sensitive polymer. Upon exposure to photons, the polymer crystallizes, triggering a coupled effect: increased stiffness in the folded beam suspensions and altered permittivity, which result in measurable shifts in resonance frequency and capacitance. Based on these mutually reinforcing effects, the proposed design is an unprecedented method for multiplying a sensor’s sensitivities for more accurate detection of gamma photons. Two preliminary devices have been fabricated and exposed to gamma radiation doses (5-35 kG) using a Co60 source; the results indicate the sensor’s elevated sensitivity (1.1 pf/G), which is higher than current state-of-the-art devices. MEMS integrated devices could replace most current conventional radiation sensors, the majority of which rely mainly on one mode of detection alone—lattice defects in single crystal silicon structures that are induced by irradiation. These defects are detected through resistance or capacitance changes. The current techniques, however, have substantial drawbacks: 1) limited sensitivity; 2) high probability of error; and 3) limited efficacy (i.e., one-time usage). To overcome these drawbacks, we introduce selective electro-deposition of gamma photon sensitive polymers on the combs and folded beam suspensions of the sensors. The mechanical design of the structure yields a more responsive sensor with a stronger output signal by coupling changes in mechanical resonance due to increased stiffness with changes in capacitance as a result of alterations in the dielectric constant of the media. Both effects work together to enhance sensitivity as well as increase the accuracy of the measurements. An SOI wafer is etched on to the front and back sides of the sensor to release the shuttle mass and expose the areas that need to be selectively coated by the gamma-sensitive polymer. Preliminary structures have been employed to test the device’s response under different gamma-ray dosages using a Co60 source ranging from 5-35 kG. Capacitance voltage characteristics and the loss factor through the dielectric layer versus the applied voltage across the dielectric media have been characterized. A sensitivity of up to 1.1 pF/G can be achieved.