Showing papers by "Benno Margesin published in 2012"

Production, characterization, and selection of the heating elements for the response stabilization of the CUORE bolometers

Abstract: One of the critical issues while operating bolometric detectors over periods of time of 1 year or more consists of keeping their response stable within a 0.1% level, despite the unavoidable temperature fluctuations of the cryogenic set-up. By using an energy pulser, which periodically delivers a fixed amount of energy in the absorber, it is possible to stabilize the response of the bolometers. A stabilization technique using heating devices, made up of heavily doped semiconductor material (well above the metal-to-insulator transition), has been developed in the framework of the CUORE experiment. In this paper we describe in detail the procedure for the realization of the heating elements, based on silicon planar technology. We then report on the multi-step low temperature characterization (77 K, 4.2 K, 1.5 K, 35 mK) of the heaters. Finally, an example of achieved stabilization for a CUORE-like detector is reported. The ∼ 1500 heaters tested at ∼ 1.5 K show less than 0.5% change in resistance between 30 μ V and 3 mV, and less than 1% change in value between 50 mK and 800 mK. In particular, the resistance change between 4.2 K and 1.5 K is less than 0.1%.

RF MEMS ohmic switches for matrix configurations

Abstract: Two different topologies of radio frequency micro-electro-mechanical system (RF MEMS) series ohmic switches (cantilever and clamped–clamped beams) in coplanar waveguide (CPW) configuration have been characterized by means of DC, environmental, and RF measurements. In particular, on-wafer checks have been followed by RF test after vibration, thermal shocks, and temperature cycles. The devices have been manufactured on high resistivity silicon substrates, as building blocks to be implemented in different single-pole 4-throw (SP4 T), double-pole double-throw (DPDT) configurations, and then integrated in Low Temperature Co-fired Ceramics (LTCC) technology for the realization of large-order Clos 3D networks.

Gold-based thin multilayers for ohmic contacts in RF-MEMS switches

Abstract: In RF-MEMS switches many reliability issues are related to the metal contacts in the switching area. The quality of this contact strongly influences switching failures due to wear, adhesion and stiction. Gold is widely used as contact material, but is a soft metal. Contact hardness can be improved preserving good conductivity and chemical inertness alternating gold layers with thin layers of other metals. A detailed study of mechanical, electrical and morphological properties of gold–chromium, gold–platinum and gold–palladium multilayers is presented and discussed. Annealing treatments modify hardness values, but a careful choice of the alloying metal is essential because hardness is reduced upon exposure to plasma ashing, a very frequent microfabrication process. This treatment also increases contact roughness, deteriorating the contact surface. Platinum is the only metal tested that is unaffected by plasma oxidation, and it also reduces the diffusion of chromium adhesion layer on the contact surface.

High-power high-contrast RF MEMS capacitive switch

Abstract: This paper reports on the first RF MEMS capacitive switch with a capacitance ratio of 130 that is stable almost up to 3 W of RF power. From an RF point of view the device behaves as a shunt capacitive switch, but employs an ohmic contact between the movable membrane and a floating metal deposited on the dielectric-coated stationary electrode, which is used to provide a high and repeatable ON state capacitance. In addition strain-relief anchor springs guarantee almost stable performances at high temperature and high power.

Electrical characteristics of floating electrode MEMS capacitive switches

Abstract: The present paper investigates in depth the electrical behaviour of floating electrode MEMS switches when their actuation is performed through the transmission line. The study is carried out through modeling and experimentally obtained capacitance- and current-voltage characteristic. It is demonstrated for the first time that constant down state capacitance is achieved without contacting the floating electrode with the moving armature. Moreover the pull-in and pull-out conditions are discussed in details.

Characterization and Modeling of Charging Effects in Dielectrics for the Actuation of RF MEMS Ohmic Series and Capacitive Shunt Switches

Abstract: Charge accumulation in dielectrics solicited by an applied voltage, and the associated temperature and time dependencies are well known in scientific literature since a number of years [1]. The potential utilization of materials being part of a device useful for space applications is a serious issue because of the harsh environmental conditions and the necessity of long term predictions about aging, out-gassing, charging and other characteristic responses [2], [3]. Micro-mechanical Systems (MEMS) for RF applications have been considered for sensor applications as well as for high frequency signal processing during more than one decade [4], [5], [6], [7], [8], [9]. In this framework, RF MEMS switches are micro-mechanical devices utilizing, preferably, a DC bias voltage for controlling the collapse of metalized beams [8]. Magnetic [10], thermal [11] and piezoelectric [12] actuations have been also evaluated, but the electrostatic one seems to be until now preferred for no current flowing, i.e. a virtual zero power consumption, less complicated manufacturing processes and more promising reliable devices [13]. During the last few years, several research activities started to release the feasibility of RF MEMS switches also for Space Applications [14], [15], [16]. The electrostatic actuation of clamped-clamped bridges or cantilevers determines the ON and OFF states depending on the chosen configuration. As well established, RF MEMS switches are widely investigated for providing low insertion loss [8], no or negligible distortion [17], [18] and somehow power handling capabilities [19], [20], [21], [22] for a huge number of structures already utilizing PIN diodes for high frequency signal processing. Actually, redundancy switches as well as single pole multiple throw (SPMT) configurations, [23], [24], matrices [25] true time delay lines (TTDL) [26], [27] and phase shifters [28], [29] for beam forming networks in antenna systems could benefit from their characteristics. On the

Thermocompression bonding for 3D RF MEMS devices using gold and silver as intermediate layer

Abstract: The paper presents preliminary results on Au-Au and Ag-Ag thermocompression bonding at low temperature. For both materials, sample structures have been prepared and different bonding conditions experimented. Results are compared in order to evaluate Au and Ag bond strength and to establish the optimum parameters. Shear tests were performed to quantify the bond strength and after that SEM was employed to examine the bonded joints. Bond strength of Ag-Ag compare to Au-Au (at 300°C and under the pressure of 0.196 MPa) seems more promising.

Modeling of gold microbeams as strain and pressure sensors for characterizing MEMS packages

Abstract: This work presents the modeling of gold microbeams for characterizing Micro-electro-mechanical systems (MEMS) packages in terms of both strains induced to the MEMS devices and hermetic sealing capability. The proposed test structures are based on arrays of rectangular-shaped clamped-free and clamped–clamped beams, to be realized with a film of electroplated gold by surface micromachining technology. The resonant frequency of the microbeams is modeled by FEM simulations as a function of substrate deformations, which could be induced by the package. Clamped–clamped bridges show a linear change of the square of the resonant frequency in case of in-plane deformations, in fairly good agreement with an approximate analytical model. Cantilever beams are modeled as variable capacitors to detect out-of-plane deformations. Finally, an analytical model to study cantilever beams as resonators for detecting pressure changes is discussed and compared with preliminary experimental results, showing an impact on the quality factor in a range from 10−2 mbar to 1 bar.

High power SP4T MEMS switch for space applications

Abstract: This paper presents the development of a fully packaged and connectorized SP4T MEMS switch for space applications. The device is provided with metal hermetic box, SSMA and SMA connectors and space qualified DC-DC Converter to operate with standard 0–5V signals. The fully packaged switches show insertion loss better than 0.65dB and isolation better than 50dB up to 240MHz. Power handling capability up to 2.5W was demonstrated during the 160h of the applied burn-in test. The devices has been developed by RF Microtech (Perugia - Italy), FBK (Fondazione Bruno Kessler - Trento - Italy) and Optoi Microelectronics (Trento - Italy).

Through wafer via holes manufacturing by variable isotropy Deep RIE process for RF applications

Abstract: This paper reports a method on the manufacturing of through silicon wafer via holes with tapered walls by Deep Reactive Ion Etching using the opportunity to change the isotropy in the DRIE equipments during processing. By using consecutively anisotropic and isotropic etching steps it is possible to enlarge the dimension of via holes on one side of the wafer, while on the other side dimension is set by the initial etching window. The optimized process was used to obtain via’s with a good control over the walls angles for two etching windows sizes (100 and 20 μm respectively) on 300 μm thick silicon wafers. After process optimization, a deviation smaller than 10% of the manufactured via holes across the wafers was observed for the designed walls angles of 11.3° and 21.8°. Barrier and seed layers were deposited in via’s performed by Physical Vapor Deposition techniques with a very good coverage of the walls. Finally, gold electroplating was used to fill the narrow part of via’s.

Wafer resistivity influence over DRIE processes for TSVs manufacturing

Abstract: This paper presents for the first time influence of the silicon resistivity over the DRIE processes. Our aim was to develop a new process for tapered walls through silicon vias (TSVs) with a good control over the walls angle. Different wafer types were used and a dependency of resistivity was found, with an important impact over the TSVs shape. Solution found is presented and experiments performed to obtained designed TSVs.

Tapered walls via holes manufactured using DRIE variable isotropy process

Abstract: This paper describes a method to manufacture through wafer via holes with tapered walls for RF applications. The main purpose was the need to obtain via holes with tapered walls that allow depositing seed and barrier layers by Physical Vapor Deposition (PVD) to enable gold electroplating. Method consists in consecutively using of the two basic process types for DRIE technique: isotropic and anisotropic etchings. Thus via holes with 20μm and 100μm diameter having tapered walls with angles between 14° and 18° were manufactured. Thin metal layers were also deposited on the walls by e-beam technique.