5.3 Wafers

L1 Phenomenon

A poled boule is sliced, lapped, and polished into wafers; flats on the wafer edge encode the crystal axes. The cut names the crystal axis normal to the wafer surface. Optics uses x-cut and z-cut wafers; phone filters use a Y-cut rotated by 128 degrees about X, reported in 1976 as the optimum rotated cut for surface-acoustic-wave substrates.

Wafer cut and crystal axesX-cut, Y-prop

          .............          
      .....           .....      
    ...                   ...    
  ...                       ...  
 ..             ^             .. 
..              |              ..
..              |              ..
..              +---->         ..
..                             ..
..                             ..
 ..                           .. 
  ...                       ...  
    ...                   ...    
      .....           .....

x (prop.) = +Y
y (in plane) = +Z
normal = +X; flat drawn at the bottom template

Normal n (crystal X, Y, Z)	(+1.000, +0.000, +0.000)	derived
Propagation x	(+0.000, +1.000, +0.000)	derived
In-plane y	(+0.000, +0.000, +1.000)	derived
Euler α, β, γ	+180.0° +90.0° +90.0°	derived
r_eff TE, lateral field	+30.80 pm/V	derived
r_eff TE, vertical field	+0.00 pm/V	derived
r_eff TM, lateral field	+8.60 pm/V	derived
r_eff TM, vertical field	+0.00 pm/V	derived

Cut

named

Rotation θ (rotated Y)128.0°

θ = 0°: Y-cut; 90°: Z-cut; 128°: the SAW cut P(title). Diameters 76.2, 100, 150, 200 mm; 128° Y LN 350 µm (4 inch) and 500 µm (6 inch) F. r: Turner 1966, clamped, 633 nm P-comp

Cut

Rotated Y-cut angle θ128.0°

Wafer normal: (+1.000, +0.000, +0.000)
TE, lateral field: +30.80 pm/V
TE, vertical field: +0.00 pm/V
TM, lateral field: +8.60 pm/V
TM, vertical field: +0.00 pm/V
Propagation x: (+0.000, +1.000, +0.000)
In-plane y: (+0.000, +0.000, +1.000)
Euler α, β, γ: +180.0° +90.0° +90.0°

Disc: wafer plane (flat edge: template); green: wafer normal; dashed: hexagonal prism with c along Z. Propagation along X for the rotated cuts; θ = 0° is the Y-cut and 90° the Z-cut. r: Turner 1966, clamped, 633 nm P-comp; r_eff derived.

Drag θ from 0° (Y-cut) toward 128° to land on the SAW cut. derived

Process viewer stepsopen in the Process viewer

#	STEP	ROUTE
05	Orient, flat, and slice into x-cut wafers	ridge
06	Lap and polish (optical grade)	ridge

                                                
                                                
                                                
                                                
                                                
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Step progress t1.00

Step

Step progress1.00

5/23Orient, flat, and slice into x-cut wafers (ridge route)

L2 Model and data

Cut	Normal	Main use	Source; status
x-cut	X	TFLN modulators: TE mode and in-plane field along Z use r₃₃	P
z-cut	Z	Bulk PPLN and APE waveguides (domains inverted through the thickness); TM modes in thin film	P, P
y-cut	Y	Proton exchange in benzoic acid damages the y-cut surface	P(abs)
128° rotated Y, X-propagating (128 Y-X)	Y rotated 128° about X	SAW filters; optimum cut reported in 1976	P(title), V
36-50° rotated Y LiTaO₃		SAW (LT, not LN)	V

Wafer specification	Value	Source; status
Diameters in production	4 and 6 inch (one SAW-wafer maker); 8-inch LN claimed in mass production by one grower	V, V
Thickness, 128 Y LN	350 µm at 4 inch, 500 µm at 6 inch	Sumitomo Metal Mining V
Donor thickness used for LTOI	525 µm (LiTaO₃)	P
Flat lengths, TTV, bow, warp, LTV, roughness	not found in a primary or standard text as of 2026-10-25	N/A
Standard covering SAW wafers	IEC 62276 (LN, LT, quartz, LBO, LGS); the 2012 edition added "reduced LN/LT" terms; edition 4.0 in 2025. Numerical limits not read	S
Optical vs acoustic grade (shown for LiTaO₃)	Acoustic grade is chemically reduced (annealed in carbon powder), optical grade is not; both congruent, same cost; optical grade had a narrower XRD rocking curve	P

L3 Details and open points

Flat convention: the primary-flat orientation relative to +X or -X, and the sign of +Z on the polished face, differ between vendors; each wafer's vendor drawing fixes them; the wafer-cut figure draws a template default.
Sign of Z: +Z is the face that becomes negative on compression under IEEE 176-1987; the pyroelectric sign follows once +Z is fixed P-comp.
Reduced ("black") LN for SAW is mentioned in the IEC scope; its reduction conditions for LN were not read.

← 5.2 Growing the crystal 5.4 Waveguides in bulk wafers →