S. Gropp

Multi-technology design of an integrated MEMS-based RF oscillator using a novel silicon-ceramic compound substrate

In this paper, an approach towards the realization of a hybrid MEMS-CMOS RF oscillator module using the novel silicon-ceramic (SiCer) compound substrate technology is described. Piezoelectric aluminium-nitride MEMS resonators with quality factors Q up to 2,200 and resonant frequencies of 240, 400 and 600 MHz have been investigated as frequency-selective elements. For RF-compatible hybrid-integrated assembly and packaging, the SiCer compound substrate has been adapted, promising an efficient integration of both, microelectronic and micromechanical devices, on a single carrier substrate. Multiphysical circuit design and simulations using parametrized behavioural MEMS models have been carried out, indicating stable oscillator operation at the design frequency. As one prospective application, such an oscillator module could form part of a compact and power-efficient reconfigurable RF transceiver frontend in SiCer technology, e.g., for mobile communications.

RF-MEMS-platform based on silicon-ceramic-composite-substrates

In the last few years, several Low Temperature Co-fired Ceramics (LTCC) materials with a silicon adapted Coefficient of Thermal Expansion (CTE) have been developed for direct wafer bonding to silicon. BGK (special type designation of Fraunhofer IKTS), a sodium containing LTCC was originally developed for anodic bonding of the sintered LTCC whereas BCT (Bondable Ceramic Tape) tailored for direct silicon bonding of green LTCC tapes to fabricate a quasi-monolithic silicon ceramic compound substrate. This so-called SiCer technique is based on homogeneous nano-structuring of a silicon substrate, a lamination step of BCT and silicon and a subsequent pressure assisted sintering. We present a new approach for an integrated RF-platform-setup combining passive, active and mechanical elements on one SiCer substrate. In this context RF parameters of the silicon adapted LTCC tapes are investigated. We show first technological results of creating cavities at the silicon ceramic interface for SiCer-specific contacting options as well as windows in the ceramic layer of the SiCer substrate for additional silicon processing. A further investigated platform technology is deep reactive ion etching of the silicon-ceramic-composite-substrate. The etching behavior of silicon on BCT will be demonstrated and discussed. With the SiCer technique it is possible to reduce the silicon content at the setup of RF MEMS to a minimum (low signal damping).

Electrostatic parallel-plate MEMS switch on silicon-ceramic-composite-substrates

In this work we will present the capabilities of this monolithic SiCer (silicon on ceramics) compound by producing a parallel-plate RF-MEMS switch with flexible electrodes and integrated coplanar waveguides. The series switch is one part of a LTE demonstrator and is developed in a heterogeneous process design. Here, the aim is to create a low-voltage switch for mobile use with a simple layout. The modelling and simulation of the parallel-plate switch with flexible electrodes is carried out using ANSYS (electro-mechanical simulation) and CADENCE (circuit simulation). To demonstrate the advantages of the composite substrate, the coplanar waveguides for the RF-signal and the control lines for the actuation of the electrostatic parallel plates of the switch are processed by screen printing them on the LTCC tapes before sintering the composite. The relocation of the waveguides into the LTCC avoids damping influences on RF signals by the silicon. An optimal process flowchart for modifying the silicon surface is shown through which bond areas with a homogeneous bond strength between silicon and LTCC are achieved and certain areas with cavities at the bond interface can be produced.

Hybrid-integrated RF MEMS-based reference oscillator using a silicon-ceramic composite substrate

In this paper, the design of a RF MEMS oscillator on a silicon-ceramic composite substrate using a high-Q Lamb-wave resonator as frequency-selective device is described. The MEMS resonator is designed on a 1.8 μm thick piezoelectric AlN layer, deposited on silicon using thin-film processes. The finite-element simulation results of the resonator structure are presented, and the derivation of the electrical equivalent-circuit is described. The active part of the MEMS oscillator, which was laid out in a Pierce topology, has been integrated in an application-specific integrated circuit fabricated in CMOS technology. Both, amplifying and frequency-selective parts are hybrid-integrated on a unique silicon-ceramic composite substrate, which enables a very compact high-quality module design with minimal parasitics. The MEMS oscillator serves as a technology demonstrator combining the advantages of microelectronic and microelectromechanical components towards a compact and power-efficient hybrid technology, e.g. for mobile communications or wireless sensors.

Fabrication of an RF-MEMS-Switch on a hybrid Si-Ceramic substrate

Abstract The integration of MEMS sensors, microelectronics and RF circuits including RF-MEMS is still a challenging task but becomes crucial for the Internet of Things. A wafer-level silicon-ceramic composite substrate (called SiCer, Silicon-on-Ceramics) allows new options in smart system integration. SiCer substrates combine the benefits of two different worlds of materials. The silicon substrate is a suitable material to build active MEMS devices such as switches and resonators. The ceramic substrate, a Low Temperature Cofired Ceramic (LTCC), is well-known for RF circuit integration including resistors, capacitors and coils. Both materials are co-sintered into a monolithically composite substrate. Chemical and physical modification of the silicon interface allows a low-pressure sintering and therefore new techniques for generating buried cavities at the bond interface. A carbon paste is applied on the LTCC via screen printing. After sintering, this results in a defined cavity. To demonstrate the advanta...

Investigations of Metal Systems in a Silicon Ceramic Composite Substrate for Electrical and Thermal Contacts as well as Associated Mounting Aspects

Abstract A quasi-monolithic silicon ceramic composite substrate (SiCer), allowing the advantageous combination of silicon MEMS technology with the LTCC technology represents a base substrate for new technology concepts. For the realization of such a substrate an adaptation (e. g. expansion coefficient) of the LTCC base material to silicon is required. Due to the fact that this TCE matched LTCC is not supplied with a metallization system, it is important to identify and evaluate suitable metal pastes. We present a compilation of evaluated silver- and gold-based metal pastes, as well as their characterization in terms of solderability and wire-bondability. With the use of thermal vias in combination with deep reactive ion etching to separate individual areas in the silicon layer [1], it is possible to adjust the thermal behavior of SiCer and of systems made of this substrate technology. Particularly for micro-electro-mechanical systems (MEMS) requiring high temperature gradients within the substrate materia...

Evaluation of a multiphysical RF MEMS oscillator based on LTE receiver performance requirements

A simulation methodology dealing with the complexity of multiphysical micro electro mechanical system (MEMS) models and their evaluation according to RF specification is presented. It is focused towards the evaluation of a hybrid MEMS-CMOS RF oscillator prior to its realization, based on the demodulation performance of a long-term evolution (LTE) user equipment (UE). The proposed multiphysical simulation approach enables to meet the constraints of the receiver specification, the design rules for manufacturing and the implementation with the novel silicon-ceramic composite substrate (SiCer) based on co-simulation and a parametrized behavioral model of the MEMS resonator. Thus, allowing to successfully address the constraints at the different abstraction levels of the design and manufacturing processes.