What is the total thickness of a 3.4 inch round TFT LCD 800x800?
Unpacking the Total Thickness of a 3.4 Inch Round TFT LCD 800x800
If you're looking at the 3.4 inch round TFT LCD 800x800, the total thickness is typically around 1.5 mm to 1.8 mm for the bare panel without any backlight or touch overlay. But that number jumps significantly once you factor in the full module assembly. Based on datasheets from suppliers like DisplayModule, the complete module—including the TFT glass, polarizer, backlight unit, and FPC (flexible printed circuit)—hits about 2.4 mm to 2.8 mm. For the specific model referenced in the 3.4 inch round tft lcd 800x800, the total thickness with the integrated backlight and MIPI interface is 2.6 mm ± 0.2 mm. That's a critical spec for enclosure design, especially in wearables, dashboards, or medical devices where every millimeter matters.
The glass substrate itself is the primary contributor to the thickness. Most round TFT panels in this size range use a single glass layer around 0.4 mm to 0.5 mm. The color filter glass on top adds another 0.4 mm to 0.5 mm, so the liquid crystal cell alone is about 0.8 mm to 1.0 mm. Polarizers are thin—typically 0.1 mm to 0.15 mm each—and they're laminated on both sides, adding roughly 0.2 mm to 0.3 mm total. So the bare TFT display without backlight is around 1.0 mm to 1.3 mm. The backlight unit is the real thickness driver. For a 3.4-inch round display, the edge-lit LED backlight with a light guide plate (LGP) and diffuser films adds 1.2 mm to 1.5 mm. That's because the LGP needs to be thick enough to distribute light evenly across the 800x800 pixel area, which has a diagonal of about 86.36 mm. The diffuser, prism, and reflective films stack up to 0.3 mm to 0.5 mm more. So the full module thickness is a sum of the TFT cell (1.0 to 1.3 mm), backlight (1.2 to 1.5 mm), and any adhesive or air gap (0.1 to 0.2 mm), totaling 2.4 mm to 2.8 mm.
But there's more nuance. The FPC (flexible printed circuit) is usually 0.1 mm to 0.2 mm thick, but it's often folded or bent behind the display, so it doesn't contribute to the z-height in most mounting scenarios. The MIPI connector adds another 0.5 mm to 0.8 mm if it's a zero-insertion-force (ZIF) type, but that's typically on the FPC tail, not the display body. Some designs also include a cover glass or touch sensor. If you add a capacitive touch panel (CTP), the thickness jumps by 0.8 mm to 1.2 mm for a glass-based touch sensor, or 0.3 mm to 0.5 mm for a film-based one. The total thickness with a glass CTP can reach 3.5 mm to 4.0 mm. For the bare module, though, the 2.6 mm spec is the one you need for mechanical CAD work.
Let's break down the typical thickness distribution in a table for clarity:
| Component | Thickness (mm) | Notes |
|---|---|---|
| Bottom polarizer | 0.10 - 0.15 | Standard TAC-based polarizer |
| TFT glass substrate | 0.40 - 0.50 | Alkali-free glass, 0.4 mm typical |
| Liquid crystal layer | 0.005 - 0.010 | Cell gap, negligible in total |
| Color filter glass | 0.40 - 0.50 | Same thickness as TFT glass |
| Top polarizer | 0.10 - 0.15 | With anti-glare coating |
| Air gap / adhesive | 0.05 - 0.10 | Optical clear adhesive (OCA) if bonded |
| Light guide plate | 0.80 - 1.00 | PMMA or PC, edge-lit |
| Diffuser film | 0.08 - 0.12 | Single or dual layer |
| Prism film (BEF) | 0.06 - 0.10 | Brightness enhancement film |
| Reflective film | 0.05 - 0.08 | ESR (enhanced specular reflector) |
| LED strip (on FPC) | 0.30 - 0.50 | Mounted on edge of LGP, not in z-stack |
| Total module | 2.40 - 2.80 | Without touch or cover glass |
Notice that the backlight stack alone—LGP, diffuser, prism, and reflector—is about 1.0 mm to 1.3 mm. The LED strip is on the side, so it doesn't add to the thickness. The backlight housing or bezel, if present, is usually 0.2 mm to 0.3 mm metal or plastic, but many round TFT modules use a frameless design to minimize thickness. The 3.4-inch round panel from DisplayModule uses a 0.5 mm TFT glass and a 0.5 mm color filter glass, with a total cell thickness of 1.05 mm (including polarizers). The backlight adds 1.45 mm, giving a total of 2.5 mm per the datasheet. That's consistent with the 2.6 mm ± 0.2 mm spec.
What about the active area? The 800x800 resolution at 3.4-inch diagonal means the pixel density is about 333 PPI (pixels per inch). The active area is roughly 60.6 mm x 60.6 mm (since the display is round, the active area is a circle with a diameter of about 86.36 mm, but the pixel array is square within that circle). The bezel or border around the active area is typically 1.0 mm to 1.5 mm on each side, so the overall glass diameter is about 88.4 mm to 89.4 mm. That bezel thickness doesn't affect the total thickness, but it's relevant for mechanical integration. The module's outer diameter, including the backlight housing, is usually 90 mm to 92 mm.
Temperature and humidity can affect thickness slightly. The liquid crystal layer expands or contracts with temperature, but the change is on the order of 0.001 mm per degree Celsius—negligible for most applications. The polarizers and films can swell in high humidity, adding 0.01 mm to 0.02 mm over time, but that's within the tolerance. The backlight LGP can warp if the module is exposed to temperatures above 70°C, which might increase the thickness by 0.1 mm to 0.2 mm due to bowing. So the 2.6 mm spec is for 25°C and 50% RH.
For weight, the 3.4-inch round TFT module typically weighs 12 grams to 15 grams without touch. The glass alone is about 8 grams (density ~2.5 g/cm³, volume ~0.5 mm x 88.4 mm diameter area ~0.5 x 3.14 x (44.2)^2 = ~0.5 x 6130 = 3065 mm³ = 3.065 cm³, times 2.5 = 7.66 g). The backlight adds 4 grams to 6 grams (LGP, films, LED). The FPC adds 0.5 grams to 1 gram. So the total weight is around 13 grams. That's light enough for handheld devices.
Now, let's talk about the MIPI interface. The FPC has a 30-pin or 40-pin connector with a pitch of 0.3 mm to 0.5 mm. The MIPI DSI (Display Serial Interface) uses two lanes plus a clock, with a data rate of up to 500 Mbps per lane. The FPC length is typically 20 mm to 30 mm from the glass edge, but it can be customized. The FPC thickness is 0.1 mm to 0.2 mm, but the connector adds 0.5 mm to 0.8 mm in height. That connector is usually on the back of the module, so it doesn't affect the front thickness, but it does add to the overall z-height if you're mounting the display flush with a housing. In that case, you might need a cutout for the connector.
Optical bonding is another factor. Some applications use optical clear adhesive (OCA) to bond the cover glass to the TFT module, eliminating the air gap. That adds 0.1 mm to 0.2 mm of OCA, but it reduces reflections and improves readability. The total thickness with a 0.7 mm cover glass and OCA would be 2.6 mm + 0.7 mm + 0.15 mm = 3.45 mm. That's a common configuration for smartwatches or industrial panels. The cover glass itself can be thinner (0.5 mm) or thicker (1.0 mm) depending on impact resistance requirements.
For the 800x800 resolution, the pixel pitch is 0.07575 mm (75.75 µm). That's calculated from the active area width of 60.6 mm divided by 800 pixels. The aperture ratio (the percentage of each pixel that lets light through) is typically 55% to 65% for a TFT LCD, depending on the design. The backlight brightness is usually 300 cd/m² to 500 cd/m² for indoor use, or up to 800 cd/m² with high-brightness LEDs. The backlight power consumption is about 0.5 W to 1.0 W for 6 to 8 LEDs. The LED forward voltage is 3.0 V to 3.2 V per LED, and the current is 20 mA to 30 mA per LED. So the total backlight current is 120 mA to 240 mA.
The viewing angle is another spec tied to thickness. The liquid crystal mode is typically IPS (In-Plane Switching) or FFS (Fringe Field Switching), which gives 80° to 85° viewing angles in all directions. The cell gap (the thickness of the liquid crystal layer) is about 3.5 µm to 4.5 µm for IPS, which is thinner than the 5 µm to 6 µm for TN (Twisted Nematic) modes. That thinner cell gap helps with faster response times (typically 25 ms to 35 ms for IPS) but doesn't affect the total module thickness significantly.
Let's compare the 3.4-inch round TFT to other common round displays. A 1.28-inch round TFT (like those used in smartwatches) is about 1.0 mm to 1.2 mm thick for the module. A 2.1-inch round TFT is around 1.8 mm to 2.0 mm. So the 3.4-inch at 2.6 mm is proportionally thicker because the backlight needs to be larger to cover the bigger area. The light guide plate for a 3.4-inch round display has a diameter of about 86 mm, so it needs to be thicker to maintain uniformity. The LGP thickness is typically 0.8 mm to 1.0 mm for a 3.4-inch display, compared to 0.4 mm to 0.6 mm for a 1.28-inch display. That's the main reason for the thickness increase.
For mechanical design, you need to account for the FPC bend radius. The FPC can be bent to a radius of 1.0 mm to 1.5 mm without damage, but you should avoid sharp creases. The connector height is usually 0.5 mm to 0.8 mm, so the total z-height from the back of the glass to the connector tip is about 2.6 mm + 0.8 mm = 3.4 mm if the connector is on the back. If the connector is on the side, it adds to the width, not the thickness. The datasheet for the 3.4 inch round tft lcd 800x800 shows the connector is on the FPC tail, which exits from the bottom of the module, so the thickness is only the module itself.
The polarizer thickness is worth noting because it affects the optical performance. The bottom polarizer is usually a reflective type for transmissive displays, while the top polarizer is an anti-glare type with a matte finish. The anti-glare coating adds 0.01 mm to 0.02 mm but reduces specular reflections. Some polarizers have a hard coat for scratch resistance, which adds another 0.005 mm. The total polarizer stack is about 0.2 mm to 0.3 mm.
In terms of assembly, the TFT glass and color filter glass are bonded together with a sealant that is 0.01 mm to 0.02 mm thick. The liquid crystal is injected through a fill port, which is then sealed. The sealant width is about 0.5 mm to 1.0 mm around the perimeter. The backlight is attached to the TFT cell with a double-sided adhesive tape that is 0.05 mm to 0.1 mm thick. Some modules use a metal frame or bezel to hold everything together, which adds 0.2 mm to 0.3 mm to the thickness. The DisplayModule 3.4-inch round TFT uses a bezel-less design, so the thickness is just the stack.
The operating temperature range is typically -20°C to +70°C for the LCD, and the storage range is -30°C to +80°C. At low temperatures, the liquid crystal becomes more viscous, which can increase response time, but the thickness doesn't change. At high temperatures, the polarizers can delaminate if the adhesive degrades, but that's a reliability issue, not a thickness issue. The backlight LEDs are rated for 50,000 hours at 25°C.
For the 800x800 resolution, the driver IC is typically a COG (Chip-on-Glass) type, which is mounted directly on the TFT glass. The IC is about 0.5 mm to 0.8 mm thick and 10 mm to 15 mm long. It's bonded to the glass with anisotropic conductive film (ACF), which is about 0.02 mm thick. The COG IC is usually on the bottom edge of the glass, so it doesn't affect the active area thickness. The FPC is bonded to the glass with ACF as well, with a thickness of 0.02 mm to 0.03 mm.
Finally, let's talk about the display's electrical interface. The MIPI DSI interface requires a power supply of 2.8 V to 3.3 V for the digital logic, and 5.0 V to 5.5 V for the backlight. The current draw for the logic is about 10 mA to 20 mA, and the backlight current is 120 mA to 240 mA. So the total power consumption is 0.5 W to 1.0 W for the backlight plus 0.03 W to 0.07 W for the logic. That's a total of 0