CTDMM Newsletter August 2008

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Vol 1. No.1 October 2008

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NEWSLETTER

By A. Marzuki

Technical Consultant of C-RAD Technologies


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Highlights&News

1. IC ranking (Fabless) in the world: Qualcomm, Broadcom , pleasesee at this URL for more info.

http://www.icinsights.com/news/bulletins/bulletins2008/bulletin20080801.html

2. Wireless Transfer Technology which was announced in 2006 byMIT is a fascinating research topic,http://www.mit.edu/~soljacic/wireless_power.html. Product basedon this technology is currently being pursued. So hopefully we cansee a product that recharge your batterys hand phone wirelessly inthe future!

3. Femtocell development is to configure each house as smallerversion of base station, it is another version of Picocell. Femtocell isthought could improve the cost and efficiency of the network, it willbe connected with broadband IP in house. It seems a lot of work needto be done to roll out this technology!

4. Lead-Free material is thought good to nature, is it so? Some say itcauses in increase on Tin usage, and we back to square one, as TinMining is not good for nature. What do you think?

5. Wireless PAN at 60 GHz for high definition TV is thought to offervery high speed, high data rate wireless connectivity, but thefrequency is one of the resonant frequencies of water. Unless we areshielded by metal, the frequency can be used at will, maybe atdifferent frequency? But we dont want to waste tremendous researcheffort on 60 GHz circuit design.

Please email your comments to [email protected]


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Circuit Techniques

1. Voltage reference circuit which is much smaller than standardband-gap circuit employs PTAT and CTAT current sources.

Ref1: A voltage reference circuit for current source of RFIC block,http://www.emeraldinsight.com/10.1108/13565360810889593Ref2: Low Power Bandgap Circuit, WIPO, WO 03/050847 A2

Please email your comments to [email protected]


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II. EXPERIMENT PROCEDURE

Figure 1 shows the top view and the cross-section of Si3N

4MIM capacitor. Top view shows the

bottom and top metal named metal 2 and metal 3 respectively, while the cross-section viewillustrated the thickness of the metal and insulator for the device with Si

3N

4as passivation of the

device. It consist of 100 m of GaAs substrate, 0.12 m thickness of Si 3N4 sandwiched betweenthe metal 2 and metal 3 with thicknesses 0.4 m and 3.12 m respectively. The complete

capacitor is covered by a layer of nitride with a thickness of 0.12 m which passivate the wholestructure.

New equivalent circuit is proposed to show the performance of Si3N

4MIM capacitor, but this

circuit is still in the beginning stage of the modeling process. Equivalent circuit of Si3N

4MIM

capacitor is depicted in Figure 2. Cm2

represent the parasitic effect associated with the bottom

metal or metal 2. C is the required value for the capacitor and Rloss

is the parasitic loss that

associated to C. Cm3

and Rm3

are the parasitic effect associated with the top metal or metal 3.

Finally, Csub

and Rsub

are the parasitic effect that associated with the substrate. Parasitic effect

description is explained in Table 1.


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Device measurement was performed in S-parameter environment using in-house microprobestation. The measurement result was then imported into S2P component in ADS window to

perform smith-chart plot and compared it with the proposed equivalent circuit model using thelumped elements through two port schematic simulation. Si

3N

4MIM capacitor measurement as

depicted in Figure 3 is connected to RF pad.

Table 1: Equivalent circuit descriptionDevice Description

Cm2

Capacitance between bottom metal (metal 2) and substrate

C Main value of capacitance

Rloss

Dielectric loss

Cm3

Capacitance between bottom metal and substrate

Rm3

Resistance between bottom metal and substrate

Csub

Substrate capacitance

Rsub

Substrate resistance


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III. RESULT AND DISCUSSION

S-parameter simulation result for Si3N

4MIM capacitor 70 m x 70 m is shown in Figure

4, 5 and 6 below. S(1,1) is to obtain the value of the measured data and S(3,3) indicates

the value of simulation using the proposed equivalent circuit model. In Figure 4, the dataof S(3,3) is similar to S(1,1) from 2 GHz to 15 GHz, but it starts to disperse from S(1,1)

at frequency near to 15 GHz up to 38 GHz, this situation is depicted in Figure 5. This

happens due to the value of Rsub

and Csub

which are optimized. At frequency is between

45 GHz to 50 GHz, the measured Si3N

4MIM capacitor device resonates 2 times, and we

can see that S(3,3) of the proposed equivalent circuit cannot be modelled S(1,1) precisely.

Figure 6 shows that the Si3N

4MIM capacitor is working as a capacitor solely without


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having inductance behaviour. The capacitance value for 70 m x 70 m Si3N

4MIM

capacitor is obtained through the imaginary admittance value as defined in ADS 2005 as

explained from (1) to (3), and the values are 2.157 pF for the measured device and 2.3737pF for the proposed equivalent circuit.


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Figure 7, 8 and 9 show the S-parameter simulation for 100 m x 100 m Si3N

4MIM capacitor.

From the figures, the function of S(1,1) and S(3,3) are similar to 70 m x 70 m Si3N

4MIM

capacitor. In Figure 7, S(3,3) of the proposed equivalent circuit model behaves similarly to themeasured S(1,1) data. This means that the proposed equivalent circuit model performance is very

good for larger device and higher frequency. Figure 8 shows the close up simulation of 100 m x100 m Si

3N

4MIM capacitor at frequencies above 15 GHz. From the figure, it is obtained that the

device starts to resonate at 16.88 GHz. Figure 9 shows that Si3N

4MIM capacitor is working as a

capacitor solely without having inductance effect. The capacitance values that are defined usingthe same technique stated in (1) to (3) are 4.372 pF for the measured device and 4.2905 pF for the

proposed equivalent circuit.


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The proposed Si3N

4MIM capacitor equivalent circuit model value using lumped elements is

explained in Table 2. The prime capacitance value for 70 m x 70 m is 2.3737 pF and for 100m x 100 m is 4.2905 pF. The proposed equivalent circuit model used for 70 m x 70 m doesnot perform very well at higher frequency than 15 GHz, hence the elements value of R

suband C

sub

which give the effect for high frequency must be tuned and optimized accordingly.

Table 2 Optimization results of Si3

N4

MIM capacitor equivalent circuit

Device 70 m x 70 m 100 m x 100 um

Cm2

3 fF 0.001 fF

C 2.3737 pF 4.2905 pF

Rloss

0.472 4.547

Cm3

0.1 fF 0.001 fF

Rm3

4 k 91.876

Csub

4 fF 16.4218 fF

Rsub

697 436

IV. CONCLUSION

S-parameter simulation of the proposed equivalent circuit model representing Si3N

4MIM

capacitor performed very well at high and low frequency if compared to measure Si3N

4MIM

capacitor device especially device with dimension 100 m x 100 m. Hence, some modificationof equivalent circuit model for smaller dimension (< 70 m x 70 m) Si

3N

4MIM capacitor will

be performed in the near future.


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ACKNOWLEDGEMENT

The author would like to thank TM R&D Sdn. Bhd. for providing the grant for this work underProject No: R05-0607-0. The help from Advanced RF systems Cluster is greatly appreciated for

guidance in using ADS-Momentum Simulator.

REFERENCES

[1] M. Engels and R.H. Jansen, Rigorous 3D EM Simulation and An Efficient Approximate Model of

MMIC Overlay Capacitors with Multiple Feedpoints, IEEE MTT-S International Microwave Symposium

Digest, 14-18 Jun 1993, Page(s): 757-760 vol.2.

[2] Piquet, J.; Cueto, O.; Charlet, F.; Thomas, M.; Bermond, C.; Farcy, A.; Torres, J.; Flechet, B,

Simulation and Characterization of High-frequency Performances of Advanced MIM Capacitors, Solid-

State Device Research Conference, 12-16 Sept. 2005, Page(s):497 500

[3] Masa Asahara, A Novel Approach to Modeling Metal-Insulator-Metal Capacitors Over Vias With

Significant Electrical Length, IEEE Transaction on Microwave Theory and techniques, Vol. 55, No. 4,

April 2007, Page(s) : 709 714

[4] Liu Lintao, Wnag Jiniang, Feng-Chang Lai, A New Equivalebt Circuit Model of MIM Capacitor for

RFIC, Microwave and Milimeter Wave Technology, pp. 1 3, April 2007.[5] Anders Mellberg, Jorgen Stenarson, An Evaluation of Three Simple Scalable MIM Capacitor Models,

Microwave and Techniques, vol. 54, no. 1, pp. 169 172, January 2006

[6] Lombard, P.; Arnould, J.-D.; Exshaw, O.; Eusebe, H.; Benech, P.; Farcy, A.; Torres, J.; MIM

capacitors model determination and analysis of parameter influence, IEEE International Symposium on

Industrial Electronics, Vol 3, Page(s):1129 1132, June 2005

Rasidah Sanusi received her B. Eng. degree in Electrical

and Electronic Engineering from University Putra

Malaysia (UPM) in 2002. Upon graduation she worked as a

Graduated Research Assistant (GRA) at UPM. She is

currently pursuing her Masters degree in Electronics at

the same university. In 2004, she joined TelekomResearch & Development Sdn. Bhd. as an assistant

researcher in the Microelectronis and Nano technology

group. She is currently involved in the MMICs

application design based on III-V material.

About CTDMM:A not for profit group with interest in Circuit Technique, Design Methodologyand Modeling.Contact: [email protected]

About CTDMM Newsletter: Newsletter which cover news and articles from industry andacademia. The main purpose is to share knowledge and news within the Microelectronics

players. Submit news or article to [email protected]. Authors to the articles are responsible tothe articles and have the right to his/her article and work.

CTDMM Newsletter August 2008

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