Pierre Bar

Thermally stable oscillator at 2.5 GHz using temperature compensated BAW resonator and its integrated temperature sensor

This paper presents a miniaturized 2.5GHz frequency source based on compensated BAW resonator with its integrated temperature molybdenum sensor assembled on the differential Colpitts oscillator. The presence of silicon dioxide layer having a positive temperature coefficient compared to other layers is used to reduce the resonators drift. A demonstration oscillator achieves a frequency drift of 40 ppm over a temperature range from -35degC to +85degC. The oscillators phase noise of -94dBc/Hz at 2 KHz offset from the carrier is reported.

Band Reject Filter in BAW Technology

This document shows the feasibility of a band reject filter in Bulk Acoustic Wave (BAW) technology. This type of filter is usually composed of series and shunt resonators. We present two setups centred at 2.5 GHz which measurement is agreed with simulation for rejection band. Filters give a -20 dB rejection on a bandwidth greater than 60 MHz for each topology. The best measured filter achieves a -1.4 dB insertion loss in the passband with a 200 MHz bandwidth.

Stopband filters built in the BAW technology [Application Notes]

This article presented the design of two band reject filters in the BAW technology. The two designs show different benefits. The ladder T topology has a better rejection bandwidth than the ladder topology because the bandwidth is controlled by resonance and antiresonance frequencies, which are selected by the loading layer. Moreover, the bandwidth is adjustable by the design. This setup presents a steeper rejection slope. The insertion loss can be reduced by increasing the bottom electrodes thickness. However, the fabrication process and the control of resonance frequency are more difficult since antiresonance frequencies of series resonators depend on the thickness of the loading layers.

Coupled Resonator Filters for W-CDMA Duplexer Application

This work presents the design and the measured performances of a duplexer based on bulk acoustic wave coupled resonator filter (BAW CRF) for W-CDMA application. This device is dedicated to be integrated in a RF module for cellular phone. A co-simulation methodology between a 1D acoustic model (Mason-type) and an electromagnetic solver is developed to allow a good prediction of the filter response on a large frequency range. The minimum insertion loss for the Tx and Rx filter is better than -3 dB and the isolation between Tx and Rx ports is greater than 60 dB. The rejection of the Tx filter is better than -50 dB in the Rx frequency range and is up to -67 dB in the Tx frequency range. The CRFs handle up to 27 dBm at Tx center frequency.

Thermo-mechanical study of a 2.5D passive silicon interposer technology: Experimental, numerical and In-Situ stress sensors developments

Thermo-mechanical stresses have proven to be a critical issue in a typical interposer integration and assembly flow. However the nature of passive interposer makes the integration of MOS-based stress sensors impossible. New methods are required. Using a coupling strategy between 3D Finite Element Models (FEM) and physical characterization, a method based on electrical measurement of passive stress sensors is presented here to assess stress at die- and wafer-level. Innovative combination of passive stress sensors based on rosettes of serpentine resistors have been developed and embedded to quantify local strain states in a typical interposer die. Their principle and implementation at a copper interconnect level of interposer are presented in this paper. Preliminary results are depicted, including first electrical measurements of these sensors. Electrical characterization has been performed after the back-side interconnection fabrication of the interposer. A local sensibility of each copper serpentine is highlighted. Discrepancies in the resistance values of orthogonal resistors could indicate local deformations to the environment of sensors, such as TSVs and bump pads. However, the order of magnitude of relative variation of resistance values is unexpectedly high and requires further investigations.

Nonlinear Behavior of CRF Device at High Power Level

This paper investigates the nonlinear behavior of CRF filters. First, measurements carried out on stand-alone resonators underline the impact of resonator size and loading layer thickness on linearity. Then, a comparison between a BAW filter and a CRF filter is presented regarding second order nonlinearities. Finally, the nonlinear behavior of CRF filters at high power levels has been investigated through co-integration of the CRF with a silicon PA in order to evaluate its impact in a WCDMA application.

Thermo-mechanical characterization of passive stress sensors in Si interposer

Passive stress sensors have been integrated in a silicon interposer test vehicle to investigate thermo-mechanical stress in a typical 2.5D system. The present sensors are integrated in a rosette-shape consisting of eight oriented copper serpentines acting like strain gauges. An innovative design allows theoretically the calculation of a partial stress tensor, including three planar and one out-of-plane components. Electrical measurements at wafer level, combined to FIB/SEM cross-sections, revealed a strong impact of elaboration processes on the structures electrical characteristics. Numerical simulations using finite element analysis were built to evaluated the theoretical sensitivity of copper serpentine to mechanical strains. Finally a dedicated four-point bending tool coupled with a four-terminal resistance measurement setup was fabricated to extract experimentally the values of sensors sensitivity factors. Preliminary results depicted in this paper highlight a sensitivity to stress of distinctly oriented resistors. Several identified sources of data dispersion are inherent to the present measurement configuration and prevent a reliable calculation of strain gauges so-called “gauge factors”.