**2.1.1 BAW Filter design and integration**

The filter was implemented to address the high level risk of electromagnetic interferences in the widely used ISM 2.4 GHz frequency band using Solid Mounted Resonators (SMR). The resonators in SMR structures are realized on the top of an acoustic mirror structure based on the Bragg reflector principle [16]. The resonators layers were composed of classical couple AlN-Mo. In contrast to [17], the Bragg reflector was implemented using an exclusive dielectric stack composed of SiOC:H and SixNy. The acoustical performance of the fully dielectric stack is comparable to traditional SiO2-W reflectors. However, this fully dielectric configuration strongly reduces the electrical coupling between resonators, and ensures high

An Efficient Adaptive Antenna-Impedance

**2.1.2 Miniaturized antenna** 

width and 18 mm height.

observed.

Tuning Unit Designed for Wireless Pacemaker Telemetry 227

In order to get better performance in the antenna to CMOS link, an alternative design has been also investigated to assemble the BAW filter with the antenna matching network in a same LTCC die, leading to a SiP approach. The comparison between on-probe BAW measurement and the flip-chipped BAW on LTCC is illustrated in Fig. 4 (b) where the responses are very close each other. Less than 0.2 dB additional insertion loss is

A miniaturized loop antennas for implanted medical device designed to operate at both MICS 402-405 MHz and ISM 2.4 GHz frequency bandwidths have been successfully fabricated [18-21]. As illustrated in Fig. 5, the designed rectangular loop antenna embedded in a titanium (σ=2.3×106 S/m) housing biocompatible pacemaker prototype is made of copper (σ=5.8×107 S/m) covered with a silicone layer (εr=2.8) for biocompatibility. The physical dimensions of the rectangular loop antenna are approximately equal to 29.5 mm

Medical devices require ultra low power, high performance transceiver. The design considerations of such transceivers are subjected to strong technical challenges which basic




In such medical microsystem, over specify the system consumes more energy, reduces the battery lifetime and is therefore not mandatory to improve the limited communication range. Longer range implies the design of an automatic power optimized system. Thus, the integration of an automatic antenna tuning unit should contribute to improve the budget

Fig. 5. Miniaturized loop antenna embedded in a pacemaker prototype


**2.2 Transceiver design constraints and limitations** 

periodically look for wakeup signal.

and increase the overall system reliability. - Higher data rates, reliability are targeted. - Good selectivity and interference rejection.

requirements [22] are as follows:

device.

out-of-band rejection. Zero level packaging ensures a micro-cavity on the upper side of the resonator, thanks to a released bi-layer SiO2/BCB.

The filter is based on a double-lattice topology (Fig. 3 (a)) and series inductances of maximum 1nH can be added so as to increase slightly the bandwidth, or for matching considerations. The photography in Fig. 3 (b) shows the 2.4 GHz filter. The active area is 450x225µm2, and the complete die is 1mm2. 120µm diameter areas with a 150µm pitch were prepared for bumping as well as for probe testing.

Fig. 3. Double lattice BAW filter (a) topology (b) photography

Flip-chip on CMOS and LTCC technologies were studied for the integration of the filter. As illustrated in Fig. 4 (a), flip chip on CMOS integration approach exhibits limited performances for several reasons. The CMOS technology is based on a lossy substrate which give low performances interconnects. As consequences, wide pad bumps are strongly capacitive and minimum distance between bumps and pad ring gives long and lossy lines.

Fig. 4. BAW filter responses (a) Flip chip on CMOS measurement and simulation (b) Stand alone BAW filter versus flip chip on LTCC

In order to get better performance in the antenna to CMOS link, an alternative design has been also investigated to assemble the BAW filter with the antenna matching network in a same LTCC die, leading to a SiP approach. The comparison between on-probe BAW measurement and the flip-chipped BAW on LTCC is illustrated in Fig. 4 (b) where the responses are very close each other. Less than 0.2 dB additional insertion loss is observed.
