A capacitive RF power sensor based on MEMS technology

Abstract

Wideband 100 kHz-4 GHz power sensors are presented, which are based on sensing the electrostatic force between an RF signal line and a suspended membrane. The electrostatic force, which is proportional to the square of the rms signal voltage and thus to the signal power, results in a displacement of the suspended membrane. This displacement is detected capacitively, allowing the sensing of the signal power with extremely low dissipative losses; therefore the sensor can be placed in a transmission line with negligible disturbance of the signal. Devices have been designed and fabricated successfully by aluminum surface micromachining using photoresist as the sacrificial layer. Optimization of the design with SONNET has resulted in measured return and insertion losses (S 11 and S 21 ) better than −30 dB and −0.15 dB, respectively, up to 4 GHz, and a sensitivity of 90 aF mW -1 .

Characterization of packaged inline-type radio frequency microelectromechanical systems power sensors

“…Typically, the general principle to achieve inline RF MEMS power sensors is that a certain part of the transmitted RF power is extracted by some sensing agents and detected, e.g. an insertion power sensor [2], a capacitive power sensor [3], and coupling power sensors in our group [4], with the available RF signal during the power detection, but there is very little consideration of real applications. Currently, most of commercial power sensors are applied to microwave power meters as detection components like self-heating power sensors [5][6][7] and indirectly-heating power sensors [8][9][10], but they are termination devices compared with the inline sensors and the input RF signal is completely dissipated after the detection.…”

Microcomposants électromécaniques pour la réalisation de références de tension en courant alternatif

“…À partir de dispositifs MEMS constitués de membranes, de poutres ou de bascules, les premières applications en métrologie électrique ont vu le jour vers 1995 avec les premiers convertisseurs alternatif-continu (AC-DC) constitués d'une bascule dans laquelle on réa-lise l'équilibre entre les forces électriques engendrées par des tensions AC et DC [1,2]. Par la suite, plusieurs équipes de recherche ont montré d'autres possibilités d'applications des MEMS pour la métrologie électrique : références de tension AC et DC [3][4][5][6], convertisseurs AC-DC [7,8], référence de courant et diviseur de tension basse fréquence [9,10], et capteurs de puissance haute fréquence [11][12][13].…”

Radiation imaging detectors made by wafer post-processing of CMOS chips

“…It can be easily deposited and patterned, it shows low residual stress and adhesion with SU-8 is good [46]. Aluminum was deposited by sputtering in several short steps to reduce the residual stress [47]. The wafer was taken out to the load lock of the sputtering system and vented with nitrogen to cool down the wafer after every deposition.…”

“…It finds application as passivation layer, interlayer or isolation (LOCOS, deep trench and shallow trench isolation) [91]. Non stoichiometric silicon-rich Si x N y (SiRN) is also used in MEMS [92], X-ray masks [93] and RF applications [47] to obtain low stress layers. In both cases the material is typically deposited by LPCVD (low pressure chemical vapor deposition) at a temperature between 700…”

“…In typical MEMS systems the deflection can be measured by the change of capacitance due to the mechanical deformation [47]. This technique cannot be applied in our case, as the pillar height is in the order of 50 µm the grid displacement induced by the electro-static force will produce a minimal change in the capacitance.…”