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Integrated Inductors for RF Transmitters in CMOS/MEMS Smart Microsensor Systems

View Article: PubMed Central

ABSTRACT

This paper presents the integration of an inductor by complementary metal-oxide-semiconductor (CMOS) compatible processes for integrated smart microsensor systems that have been developed to monitor the motion and vital signs of humans in various environments. Integration of radio frequency transmitter (RF) technology with complementary metal-oxide-semiconductor/micro electro mechanical systems (CMOS/MEMS) microsensors is required to realize the wireless smart microsensors system. The essential RF components such as a voltage controlled RF-CMOS oscillator (VCO), spiral inductors for an LC resonator and an integrated antenna have been fabricated and evaluated experimentally. The fabricated RF transmitter and integrated antenna were packaged with subminiature series A (SMA) connectors, respectively. For the impedance (50 Ω) matching, a bonding wire type inductor was developed. In this paper, the design and fabrication of the bonding wire inductor for impedance matching is described. Integrated techniques for the RF transmitter by CMOS compatible processes have been successfully developed. After matching by inserting the bonding wire inductor between the on-chip integrated antenna and the VCO output, the measured emission power at distance of 5 m from RF transmitter was -37 dBm (0.2 μW).

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Cross section of the spiral inductors with two metal layers in CMOS process.
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f8-sensors-07-01387: Cross section of the spiral inductors with two metal layers in CMOS process.

Mentions: Figure 7 shows the fabricated coils and LC resonator integrated on silicon for the 300-MHz frequency band. Figure 7(a) shows the fabricated integrated inductors with various layout patterns. Finally, the pattern of the inductor was optimized and used in the LC resonator, as shown in Figure 7(b). All the materials are common to standard CMOS fabrication technologies. The cross-sectional structure of the spiral inductors is shown in Figure 8. A thick (2μm) second metal layer was formed to obtain a lower resistive conductor because the resistance of the conductor degrades the Q-factor of integrated RF components, as is well known [12]. As shown in the figure, the first metal layer has two layers of 1% silicon composite aluminum and pure aluminum. The lower layer is necessary to prevent harmful reactions between the first metal layer and silicon device surface, while the upper layer is required for better contact with the second metal layer (pure aluminum). The parameters of spiral inductors are the number of sides, the space between tracks, the number of turns, the external radius, and the track widths. The performance of the spiral inductor has been satisfactory for this application of design improvement. Nevertheless, parameter extraction and further optimization will be continued to obtain higher performance. The spiral inductor was designed with the modified wideband π model [13]. An inductance of 28.1nH and a Q-factor of over 1 were the design targets. First, the fabricated spiral inductors and LC resonators were evaluated at the wafer level by RF probes for electrical checks. Then they are mounted on packages (test fixture). A Subminiature series A (SMA) connector was used between the devices under test (DUT) and the VNA. The measured Q-factor of the inductor was 0.22 at 300-MHz. The low Q-factor is due to parasitic effects such as magnetic field penetration, metal–substrate capacitance, and so on. The measured resonant frequency was about 600-MHz. When an inductor is integrated on silicon, some undesirable induced effects show up. The reason is that the metallic layers are separated from the semiconductor substrate by a layer of silicon dioxide. These effects can be classified in two types, magnetically induced [13] and electrically induced [14]. Because of the induced effects, the value of inductance will decrease and the resonant frequency becomes higher. The parasitic effect also causes impedance mismatching at the targeted carrier frequency (300-MHz in this study). Thus, an impedance matching procedure is necessary to obtain better performance of the integrated LC resonator used as an on-chip antenna for RF radiation. Improvement of the performance of the LC resonator is discussed in the next section in detail.


Integrated Inductors for RF Transmitters in CMOS/MEMS Smart Microsensor Systems
Cross section of the spiral inductors with two metal layers in CMOS process.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814858&req=5

f8-sensors-07-01387: Cross section of the spiral inductors with two metal layers in CMOS process.
Mentions: Figure 7 shows the fabricated coils and LC resonator integrated on silicon for the 300-MHz frequency band. Figure 7(a) shows the fabricated integrated inductors with various layout patterns. Finally, the pattern of the inductor was optimized and used in the LC resonator, as shown in Figure 7(b). All the materials are common to standard CMOS fabrication technologies. The cross-sectional structure of the spiral inductors is shown in Figure 8. A thick (2μm) second metal layer was formed to obtain a lower resistive conductor because the resistance of the conductor degrades the Q-factor of integrated RF components, as is well known [12]. As shown in the figure, the first metal layer has two layers of 1% silicon composite aluminum and pure aluminum. The lower layer is necessary to prevent harmful reactions between the first metal layer and silicon device surface, while the upper layer is required for better contact with the second metal layer (pure aluminum). The parameters of spiral inductors are the number of sides, the space between tracks, the number of turns, the external radius, and the track widths. The performance of the spiral inductor has been satisfactory for this application of design improvement. Nevertheless, parameter extraction and further optimization will be continued to obtain higher performance. The spiral inductor was designed with the modified wideband π model [13]. An inductance of 28.1nH and a Q-factor of over 1 were the design targets. First, the fabricated spiral inductors and LC resonators were evaluated at the wafer level by RF probes for electrical checks. Then they are mounted on packages (test fixture). A Subminiature series A (SMA) connector was used between the devices under test (DUT) and the VNA. The measured Q-factor of the inductor was 0.22 at 300-MHz. The low Q-factor is due to parasitic effects such as magnetic field penetration, metal–substrate capacitance, and so on. The measured resonant frequency was about 600-MHz. When an inductor is integrated on silicon, some undesirable induced effects show up. The reason is that the metallic layers are separated from the semiconductor substrate by a layer of silicon dioxide. These effects can be classified in two types, magnetically induced [13] and electrically induced [14]. Because of the induced effects, the value of inductance will decrease and the resonant frequency becomes higher. The parasitic effect also causes impedance mismatching at the targeted carrier frequency (300-MHz in this study). Thus, an impedance matching procedure is necessary to obtain better performance of the integrated LC resonator used as an on-chip antenna for RF radiation. Improvement of the performance of the LC resonator is discussed in the next section in detail.

View Article: PubMed Central

ABSTRACT

This paper presents the integration of an inductor by complementary metal-oxide-semiconductor (CMOS) compatible processes for integrated smart microsensor systems that have been developed to monitor the motion and vital signs of humans in various environments. Integration of radio frequency transmitter (RF) technology with complementary metal-oxide-semiconductor/micro electro mechanical systems (CMOS/MEMS) microsensors is required to realize the wireless smart microsensors system. The essential RF components such as a voltage controlled RF-CMOS oscillator (VCO), spiral inductors for an LC resonator and an integrated antenna have been fabricated and evaluated experimentally. The fabricated RF transmitter and integrated antenna were packaged with subminiature series A (SMA) connectors, respectively. For the impedance (50 Ω) matching, a bonding wire type inductor was developed. In this paper, the design and fabrication of the bonding wire inductor for impedance matching is described. Integrated techniques for the RF transmitter by CMOS compatible processes have been successfully developed. After matching by inserting the bonding wire inductor between the on-chip integrated antenna and the VCO output, the measured emission power at distance of 5 m from RF transmitter was -37 dBm (0.2 μW).

No MeSH data available.


Related in: MedlinePlus