Mirosław Maliński Department of Electronics and Computer Studies

1. APPLICATIONS OF THERMOACOUSTIC TECHNIQUES FOR THERMAL, OPTICAL AND MECHANICAL CHARACTERIZATION OF MATERIALS, STRUCTURES AND DEVICES Mirosław Maliński Department of Electronics and Computer Studies Technical Univeristy of Koszalin, Poland

2. Contents • Introduction • Multi-layer optically opaque systems • Optically semitransparent systems • Determination of thermal parameters of materials • Determination of recombination parameters of carriers • Determination of air-tightness of packagings • Investigation of the quality of the surface of samples • Investigation of composition of crystals and their quality • Determination of internal quantum efficiency

3. Introduction • Thermoacoustics uses both frequency and spectral amplitude and phase characteristicsfor determination of several parameters of samples and structures • This presentation is limited to the analysis of FA characteristics measured with a microphone or piezoelectric methods

4. The idea of a thermoacoustic method • Generation of periodical heat in the sample by absorbed light or dissipation of electric power • Propagation of induced thermal waves in the sample • Detection of the amplitude and phase of a thermal wave with one of the methods e.g. microphone, IR or piezoelectric or… • Detection of one of the effects connected with the periodical temperature distribution e.g. thermal expantion, thermoelastic bending, IR emission, overpressure

5. Schematic diagram of a sample

6. Temperature spatial distribution

7. Example temperature distributions R=1(left)R= -1 (right):1-t=0, 2-t=T/4, 3-t=T/2, 4-t=3T/4.l=0.1 cm,  =0.1 cm2/s,  =100 cm-1,f=16Hz.

8. Photoacoustic signals • Microphone detection • Piezoelectric detection

9. Experimental set-up

10. Multilayer optically opaque systems

11. Multilayer optically opaque systems

12. Multilayer optically opaque systems • Theoretical frequency domain dependencies of a phase of a photoacoustic signal for a transistor structure of a thickness l1=230 m, a lead frame of the thickness l3=350 m for different values of air delaminations: 1– 0.025 m, 2– 0.05 m, 3– 0.075 m, 4– 0.1 m, 5– 0.15 m, 6– 0.2 m.

13. Multilayer optically opaque systems • Correlation of the phase of the PA signal and the force of detachment of the transistor structure from a lead frame. Solid line is a theoretical curve, circles are experimental points, BC 237 transistor structures • Phase(S) = (180/)arg (S1( d2 = 0m)p + S2(d2 = 0.1 m)(1-p)) • Force necessary for detachment is proportional to the parameter p

14. Optically semitransparent systems • Schematic diagram of a thin semitransparent layer on the semitransparent backing • Application – characterization of thin semiconductor films on semiconductor thick substrates

15. Optically semitransparent systems

16. 0.4 40 0.3 60 PHASE [degs] AMPLITUDE [a.u] 0.2 80 0.1 100 0 100 200 300 400 500 100 200 300 400 500 FREQUENCY [Hz} FREQUENCY [Hz] Optically semitransparent systems GaAs on Si • Amplitude and phase photoacoustic frequency characteristics of a l1= 10 m thick layer on the thick substrate. Parameters taken for computations: 1=0 cm-1 , 2=10000 cm-1 (solid line), 1=104 cm-1, 2=103 cm-1 ( dash line), 1=0.3 cm2/s, 2=0.9 cm2/s, GaAs/Si

17. Optically semitransparent systems SCL in Si • Theoretical influence of a SCL on the photoacoustic amplitude and phase characteristics in the front configuration. Parameters: =0.01 cm2/s, thickness of the layer l1=5 m – dash line, l1=10 m – dotted line, l1=15 m – solid line, 1=0 cm-1, 2=1000 cm-1, R12=0.

18. Optically semitransparent systems PS on Si substrate • The phase frequency characteristics of the PS/Si structure in the reflection configuration. Diamonds and circles are for exc=514 nm and exc=670 nm. Parameters of PS layer=0.016cm2/s, kc=0.0042 cal(cmKs)-1, 1(514nm)=1900 cm-1, 1(670nm)=903 cm-1.

19. Optically semitransparent systems PS on Si substrate • d1=50m on theSi substrate of the thickness d2=500 m.The anodisation current I=100mA for the time t=10 min

20. Determination of thermal parameters

21. Determination of thermal parameters –piezoelectric method • ZnSe crystal l = 0.081 cm=0.01 cm2/s( solid line),= 0.05 cm2/s, 0.1 cm2/s, 0.2 cm2/s. • Zn0.83Be0.17Sel=0.1161 cm=0.05 cm2/s,=0.01 cm2/s, =0.1 cm2/s and = 0.2 cm2/s

22. Determination of thermal parameters –microphone method • Si samplel=240m and =0.6 cm2/s. Description of lines: line 1 – R = 1, line 2 – R = 0.9, line 3 – R = 0.76, line 4 – R = 0.5. Circles and diamonds are experimental lines, lines are theoretical curves.

23. Determination of thermal parameters 100 80 60 THERMAL CONDUCTIVITY [W/mK] 40 • Dependance of the thermal conductivity of SiGe on the composition 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 CONCENTRATION of Si in SiGe

24. Determination of recombination parameters in TWI-PW model

25. Determination of recombination parameters • Computations of Ge samples: = 0.4 cm2/s, l = 0.1 cm, = 2010-6 s, D = 44 cm2/s, V = 500 cm/s a) = 0.110-6 s and D = 22 cm2/s b).

26. 3.5 100 3 50 2.5 AMPLITUDE RATIO [a.u.] PHASE SHIFT [degs] 2 0 1.5 1 50 0.5 3 . 3 . 10 100 1 10 10 100 1 10 FREQUENCY [Hz] FREQUENCY [Hz] Determination of recombination parameters • SiGe: =0.37 cm2/s, L=0.1 cm, E1=2.0 eV, E2=1.4 eV, Eg=1.1 eV, D=44 cm2/s, V=800 cm/s, = 100 s

27. Air-tightness measurements

28. Air-tightness measurements- theoretical model • Parameters taken for computation:  = 1710-6 [Ns/m2], L = 6-4 [m], M = 2810-3 [kg/mole], V2 = 2.1610-6 [m3], V2/V1 = 3.19, r = 20 m...60 m,  = 1.3 [kg/m3], Na = 610-23 [mole-1], T = 300 K, k = 1.3810-23 [J/K].

29. 1 0.9 1 0.8 0.7 2 0.6 0.5 AMPLITUDE RATIO [1] 3 0.4 0.3 4 0.2 0.1 5 6 0 10 100 log (f) Air-tightness measurements -poster • 1) r = 108m; 2) r = 91m;3) r = 78m; 4) r = 69m; 5) r = 42m;6) r =24m; L.Majchrzak, M.Maliński ‘Analysis of a Thermoacoustic Approach for the Evaluation of Hermeticity of Packaging of Electronic Devices’ XXIV IMAPS Poland Conf2005

30. Determination of the quality of the surface p-type Si • Theoretical and experimental piezoelectric spectra of p-Si at RTd=0.0037 cm, d=0.0050 cm.

31. Determination of the surface quality • Amplitude PPT spectra of CdTe sample at f = 76 Hz. Circles – experimental results, and a solid line is the theoretical curve: Eg = 1.51 eV,  = 0.03 cm2s-1,  = 0.0019 cm, 0 = 130 cm-1,  = 0.9.

32. Composition of mixed crystals • The correlation of the energy gap value of the Zn 1-xBexTe mixed crystal and the mole fraction of beryllium x in the crystal

33. 8 150 100 6 50 4 AMPLITUDE [j.u.] PHASE[deg] 0 2 – 50 – 100 0 2.0 2.2 2.4 2.6 2.0 2.1 2.2 2.3 2.4 2.5 ENERGY [eV] ENERGY [eV] Composition of mixed crystals • Zn0.93Be0.07TeEg1 = 2.31eV, Eg2 = 2.380 eV , k = 0.4, = 0.2cm2/s, f = 36 Hz,  = 0.005 cm, R = 1

34. Internal quantum efficiency • Schematic diagram of the absorption and irradiative and radiative recombination processes involved in a generation of the photoacoustic signal.

35. Internal quantum efficiency • ZnTe RT at 76 Hz and 126 Hz, internal quantum efficiency of irradiative recombination R=0.75

36. Conclusions • Frequency FA characteristics are a useful tool bringing information about: • Multilayer optically opaque systems • Optically semitransparent systems • Thermal parameters of materials • Recombination parameters of carriers • Air-tightness of packagings • Determination of the quality of the surface and composition • Determination of the internal quantum efficiency

37. Thank You for Your attention