Layer Guided SH-APM Sensors

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1 Layer Guided SH-APM Sensors Gen McHae, M. I. Newton and F. Martin Department of Chemistry and Physics The Nottingham Trent Uniersity Nottingham NG 8NS, UK Acknowedgements Dr Eectra Gizei and Dr Kathryn Mezak, Institute of Biotechnoogy, Cambridge Uniersity BBSRC (Grant 30/E40)

2 Oeriew. Acoustic Wae Sensor Principes QCM SAW Vapour phase response Liquid phase response 2. Layer Guided Acoustic Waes Loe waes SH-APMs Generaized dispersion cure Mass sensitiity Group and phase eocity 3. Loe Waes and Frequency Frequency dependence Frequency hopping 4. Summary

3 Sensing Principes Quartz Crysta Microbaance (QCM) Thickness shear mode osciation Surface Acoustic Wae (SAW) Mechanica wae traeing aong a surface Create Resonator or Measure Impedance/Spectrum QCM/SAW determines osciation freq. fλ Mass (thin fim) oading Main effect is change in frequency δf ρf 2

4 Surface oading aters resonance Mass oading reduces frequency Non-rigid mass (e.g. poymers) broadens resonance (senses shear moduus) Liquid oading and penetration depth Need shear modes (QCM, Shear type SAWs) Senses mass in penetration depth δf (ηρ (ηρ) f /2 For water penetration depth ~ 250 nm (at 5 MHz)

5 Loe Waes SH-APMs Surface Acoustic Wae (SAW) Loe Wae Layer guided SH-SAW with < s SH-APM Substrate resonance

6 Loe Waes 6000 Theoretica dispersion cure (Insertion oss is unchanged by guiding ayer) Dispacements for first three modes (z.3) P hase Spee d D ispacement o f aye r z is dê First mode Third mode Second mode x3êd

7 Boundary conditions dispersion eqn where ξµ s T s /µ T, k (ω/) /2 and and Layer Guided SH-APMs Generaized Dispersion Equation Layer and substrate dispacements Eqns of motion T and T s McHae et a, Accepted Europhys. Lett. (2002), J. App. Phys. (2002) 9, [ ] ( ) 3 3 (0,,0) x k t j x jt x jt e Be Ae u + ω [ ] ( ) 3 3 (0,,0) x k t j x T x T s e De Ce u s s + ω T ω s s T ω ) tanh( ) tan( w T d T s ξ

8 Soutions T s rea < s "Loe" Waes T s jk s with k s rea > s "Layer guided SH-APMs" Eoution of st SH-APM P hase S pee d, m s dê Points Anti-node moing from substrate to ayer APM s s Loe Waes Dispacement Dispacement x 3 êw x 3 êd

9 Mass Sensitiity (Arb. d) - with 3 ayer mode S m im m 0 m o fo ρ d og dz e z 0 m is mass per unit area being sensed, zdf/ is the normaized thickness "Rigid" mass Mass sensitiity is sope of dispersion Loe Waes Layer-Guided SH-APMs S ensitiity,»sm» m 2 k g S ensitiity,»s m» m 2 k g dê dê McHae et a, J. App. Phys. Accepted (2002).

10 Preiminary Experimenta Data Dispersion Cure Experiment Prop. Orthog. to x-axis of thinned (200 µm) ST-Q substrate 0 MHz surface skimming buk wae (SSBW) SSBW Loe wae by a spin-coated photoresist ayer Od mask so insertion oss high (axis is d/λ with λidt period) Frequency, MHz d/ λ

11 Dispersion and Group Veocity Guiding Layer Induced Dispersion Phase eocity fλ or ω/k Group eocity g dω/dk Group eocity is sope of the (ω, k) dispersion cure w n s Exampe 0.25 µm poymer guiding ayer on Quartz with w Substrate speed Layer speed a n d g m s g k mm dê Submitted to J. App.Phys. (2002)

12 Mass Sensitiity and Dispersion S m ρd g ρ d ( ) g g "Rigid" mass Mass sensitiity is fractiona deiation of the phase eocity from the group eocity diided by mass per unit area due to the guiding ayer Define a Group Veocity Sensitiity S g m fo ρ d og e dz g z z o»sm» a n d»sm g» m 2 k g Group sensitiity Phase sensitiity dê

13 Loe Waes and Higher Frequency Estabished QCM Sensor Principe Mass sensitiity Fundamenta frequency Higher frequency Higher mass sensitiity Loe Waes on a (Semi-) Infinite Substrate Controing dimensioness ariabe is z d/λ df/ S m im m 0 m o f o ρ d og dz e z 0 Mass Sensitiity Frequency Function of z o Normaized thickness at operating point z o d f

14 Higher Frequency Operation,2 Routes Issues. Increase fundamenta frequency. Change of Loe wae mode? 2. Hop the frequency to a harmonic 2. Const. guiding ayer thickness? Frequency Increase at Constant z o Reduce d as /f No change on dispersion cure Mass sensitiity scaes with f Frequency Hopping at Constant d Four exampe transitions Same mode ower/higher sensitiity Change mode ower/higher sensitiity P hase S pee d, m s z 0 z z 2 z 3 a) c) d) b) dê M.I. Newton et a, Eectron. Lett. 36 (200) ; 2 G. McHae et a, J. App. Phys.Accepted (2002)

15 Frequency Hopping Transitions 6000 z 0 z z 2 z 3 P hase S pee d, m s a) c) b) d) No Mode Change dê Mode Change Transition a) Higher mass sensitiity Transition b) Lower mass sensitiity Transition c) Lower mass sensitiity Transition d) Higher mass sensitiity Maximum Increase in Mass Sensitiity Ratio of frequencies ratio of max sopes of modes i.e. scaes by ess than by the frequency ratio

16 Summary Achieements Unifying theory Loe wae and SH-APM's New sensor Layer-guided SH-APM's Mass sensitiity predictions Phase eocity Reation to group eocity Loe wae frequency response Mode and non-mode changes Lessons Higher order Loe waes from SH-APM's Guiding ayer on SH-APM's significant increase in sensitiity Higher frequency Higher or ower sensitiity Frequency scaing of mode peak Loe waes strong dispersion Group and phase eocity differ The End

Gas and Liquid Phase Sensitivity of Love Waves

Gas and Liquid Phase Sensitivity of Love Waves Gas and Liquid Phase Sensitiity Le Waes Gen McHae, M. I. Newtn and F. Martin Department Chemistry and Physics The Nttingham Trent Uniersity Nttingham NG 8NS, UK Acknwedgements Dr Eectra Gizei and Dr Kathryn